Bimodal polyethylene composition and articles made therefrom

ABSTRACT

The invention relates to a polyethylene composition with a bimodal molecular weight distribution and articles made therefrom, such as high topload blow moldings and transmission and distribution pipes. The composition comprises a low-molecular-weight (LMW) ethylene homopolymer component and a homogeneous, high-molecular-weight (HMW) ethylene interpolymer component, wherein the LMW component is characterized as having a molecular weight distribution, MWD L , of less than about 8. The composition is characterized as having a bimodal molecular weight distribution, and a ductile-brittle transition temperature, T db , of less than −20° C. In some embodiments, the HMW component is characterized by a reverse comonomer distribution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSerial No. 60/313,357 filed on Aug. 17, 2001, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a high density polyethylene composition with abimodal molecular weight distribution and articles made therefrom,especially high topload blow moldings and high temperature or highpressure, long duration pipes.

BACKGROUND OF THE INVENTION

Polyethylene pipes are light in weight, easy to handle, and arenon-corrosive. In addition, their rigidity is relatively high that theycan be laid under the ground, and their flexibility is also relativelyhigh that they can follow a movement of ground. Due to theseadvantageous characteristics, the amount of polyethylene pipes used israpidly increasing in recent years.

In addition to the above desirable characteristics, polyethylene pipesshould have (1) impact resistance sufficient to endure impacts given atthe time when and after they are set; and (2) excellent long-termdurability under gas or water pressure (specifically, environmentalstress cracking resistance and internal pressure creep resistance).

With respect to the long-term durability, conventional pipes may meetthe ISO standard, i.e. 50-year durability at normal temperatures underan internal pressure, expressed in terms of circumferential stress, ofapproximately 8 MPa. However, the conventional polyethylene pipes arestill insufficient in the long-term durability for use under more severeconditions, such as main pipes for gases or running water which have alarge diameter and undergo high internal pressure. For this reason, theyare presently used only for branch pipes and the like, having a smalldiameter.

The long-term durability of a polyethylene pipe is considered to bedetermined by the environmental stress cracking resistance, that is theresistance to cracking which is caused when an internal pressure appliedto the pipe acts as a tensile stress in the circumferential direction onthe pipe over a long period of time. Therefore, in order to improve thelong-term durability of polyethylene pipes, it is necessary to improvethe environmental (tensile) stress cracking resistance.

For plastic pipe applications, circumferential (hoop) stress performanceas set forth in ISO 9080 and ISO 1167 is an important requirement. Theseprocedures describe the long-term creep rupture behavior of plasticmaterials by an extrapolation methodology wherein the hydrostaticstrength of pipe materials over 50 years at 20° C. are predicted.Typically, for long term predictive performance testing, candidate pipematerials are placed at various stresses and the lifetime at a giventemperature is determined. For extrapolations to 50 years at 20° C.,testing is also performed at higher temperatures. The measured lifetimecurves at each temperature typically consists of either a high stress,lower lifetime ductile failure mode or a lower stress, longer lifetimebrittle failure mode. The ductile failure mode is referred to as Stage Ifailure and conversely the brittle failure mode is referred to as StageII failure.

First and second generation polyethylene pipes for water and gasdistribution have minimum required strength (MRS) ratings for respectivehoop stresses of 6.3 and 8 MPa and are known as PE63 and PE80,respectively. Third generation polyethylene pipes, which are known asPE100 pipes, conform to a MRS rating of 10. The MRS rating is based onthe above ISO procedures wherein a MRS rating of 10 specifies that pipesmade from the polyethylene materials must withstand 10 MPa at 20° C. for50 years.

Another important pipe or durable material performance requirement isresistance to rapid crack propagation (RCP). The RCP of a pipe materialis typically measured by testing extruded pipe in accordance with ISO13477 (the so-called ‘S4’ test). But the S4 test is not susceptible tosmall scale evaluation and as such various small scale tests have beenintroduced in the plastic pipe industry. Small scale testing includesthe inverted Charpy test and the Plane High-Speed Double Torsion test,as well as ranking tests such as a critical strain energy release ratetest or G_(c) measurement on compression molded materials. Also, thelower the ductile to brittle transition temperature, T_(db), of amaterial, the better is its RCP resistance.

In order to improve the environmental stress cracking resistance of apolyethylene composition, it is known to increase the molecular weightor to decrease the density of the polyethylene. However, when themolecular weight is increased, the fluidity of the polyethylene islowered, so that the molding properties such as pipe-extrusionproperties and injection moldability are impaired. When the density isdecreased, the rigidity of the polyethylene is unfavorably lowered.

Although numerous pipe compositions have been known and used, therecontinues to exist a need for improved durable materials, especially fortransmission and distribution pipe service for gases and water.Preferably, the materials should exhibit improved durability and/orhigher temperature service lives. In particular, there is still a needfor high density polyethylene durable materials with better resistanceto slow crack propagation and/or rapid crack propagation.

SUMMARY OF THE INVENTION

We have discovered a bimodal high density polyethylene composition thatexhibits improved durability. The new composition comprises at least alow-molecular-weight (LMW) ethylene homopolymer component having amolecular weight distribution, MWD^(L), of less than about 8 and ahomogeneous, high-molecular-weight (HMW) ethylene interpolymercomponent. The composition is characterized as having a bimodalmolecular weight distribution and a ductile-brittle transitiontemperature, T_(db), of less than −20° C. Preferably, the overallM_(w)/M_(n) (indicative of the molecular weight distribution or MWD) ofthe novel composition is relatively narrow, and the M_(w)/M_(n) of theLMW component is relatively narrow, or the MWD for both the LMWcomponent and the HMW component is also relatively narrow, or the MWD ofthe each component is relatively narrow and completely distinct from oneanother. In some embodiments, the HMW component is characterized by a“reverse comonomer distribution.”

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are plots of molecular weight distribution for bimdoalpolymers in accordance with embodiments of the invention.

FIG. 2 is a schematic of the creep rupture testing rig used to evaluateinventive examples.

FIG. 3 is a plot of G_(c) versus PENT performance for Inventive Example6 as compared to standard PE 100 and PE80 resin performance.

FIG. 4 is a plot of RCP (based on G_(c) data) for inventive examples andcomparative runs.

FIG. 5 is a plot of creep rupture performance for inventive examples andcomparative runs.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention provide a new polyethylene compositionwhich can be used for making water or oil pipes and other products. Thenew composition comprises a low-molecular-weight (LMW) ethylenehomopolymer component and a high-molecular-weight (HMW) ethyleneinterpolymer component. The new composition is characterized by arelatively narrow bimodal molecular weight distribution. The bimodalityof the molecular weight distribution of the new composition is due tothe difference in the MWD of the LMW component and the HMW component.Preferably, the MWD of the LMW and HMW components individually isunimodal but is different and distinct from each other such that, whenmixed, the resulting composition has an overall bimodal molecular weightdistribution. The LMW ethylene homopolymer component has a molecularweight distribution, MWD^(L), of less than about 8 and the newcomposition is characterized as having a ductile-brittle transitiontemperature, T_(db), of less than −20° C. In some embodiments, the HMWcomponent is characterized by a substantially uniform comonomerdistribution or a reverse comonomer distribution

In the following description, all numbers disclosed herein areapproximate values, regardless whether the word “about” or “approximate”is used in connection therewith. They may vary by 1%, 2%, 5%, andsometimes, 10 to 20%. Whenever a numerical range with a lower limit,R^(L) and an upper limit, R^(U), is disclosed, any number falling withinthe range is specifically disclosed. In particular, the followingnumbers within the range are specifically disclosed:R=R^(L)+k*(R^(U)−R^(L)), wherein k is a variable ranging from 1% to 100%with a 1% increment, i.e., k is 1%, 2%, 3%, 4%, 5%, . . . , 50%, 51%,52%, . . . , 95%, 96%, 97%, 98%, 99%, or 100%. Moreover, any numericalrange defined by two R numbers as defined in the above is alsospecifically disclosed.

The term “substantially uniform comonomer distribution” is used hereinto mean that comonomer content of the polymer fractions across themolecular weight range of the HMW component vary by less than 10 weightpercent, preferably 8 weight percent, 5 weight percent, or 2 weightpercent.

The term “homogeneous polymer” is used herein refers to polymerizationproducts of relatively narrow molecular weight distribution andexhibiting a comonomer content of chains having the substantially thesame molecular weight does not vary substantially from chain to chain,in other words the polymers exhibit a relatively even sequencing ofcomonomers within a chain at a given molecular weight.

The term “reverse comonomer distribution” is used herein to mean acrossthe molecular weight range of the HMW component, comonomer contents forthe various polymer fractions are not substantially uniform and thehigher molecular weight fractions thereof have proportionally highercomonomer contents. Both a substantially uniform and a reverse comonomerdistribution can be determined using fractionation techniques such asgel permeation chromatography-differential viscometry (GPC-DV),temperature rising elution fraction-differential viscometry (TREF-DV) orcross-fractionation techniques.

The term “bimodal” as used herein means that the MWD in a GPC curveexhibits two component polymers wherein one component polymer may evenexist as a hump, shoulder or tail relative to the MWD of the othercomponent polymer. A bimodal MWD can be deconvoluted into twocomponents: LMW component and HMW component. After deconvolution, thepeak width at half maxima (WAHM) and the average molecular weight(M_(w)) of each component can be obtained. Then the degree of separation(“DOS”) between the two components can be calculated by the followingequation:${DOS} = \frac{M_{w}^{H} - M_{w}^{L}}{{WAHM}^{H} + {WAHM}^{L}}$

wherein M_(w) ^(H) and M_(w) ^(L) are the respective weight averagemolecular weight of the HMW component and the LMW component; andWAHM^(H) and WAHM^(L) are the respective peak width at the half maximaof the deconvoluted molecular weight distribution curve for the HMWcomponent and the LMW component. The DOS for the new composition isabout 0.01 or higher. In some embodiments, DOS is higher than about0.05, 0.1, 0.5, or 0.8. Preferably, DOS for the bimodal components is atleast about 1 or higher. For example, DOS is at least about 1.2, 1.5,1.7, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0. In some embodiments, DOS isbetween about 5.0 to abut 100, between about 100 to 500, or betweenabout 500 to 1,000. It should be noted that DOS can be any number in theabove range. In other embodiments, DOS exceeds 1,000. Of course, in someembodiments, a “bimodal molecular weight distribution” may bedeconvoluted with the freedom to fit more than two peaks. In someembodiments, the term “bimodal” does not include multimodal polymers,for example LDPE.

The term “unimodal” as used herein in reference to the overall MWD ofcomparative examples or in reference to the MWD of a component polymerof the inventive composition means the MWD in a GPC curve does notsubstantially exhibit multiple component polymers (i.e., no humps,shoulders or tails exist or are substantially discernible in the GPCcurve). In other words, the DOS is zero or substantially close to zero.

The term “distinct” as used herein in reference to the molecular weightdistribution of the LMW component and the HWM component means there isno substantial overlapping of the two corresponding molecular weightdistributions in the resulting GPC curve. That is, each molecular weightdistribution is sufficiently narrow and their average molecular weightsare sufficiently different that the MWD of both components substantiallyexhibits a baseline on its high molecular weight side as well as on itslow molecular weight side. In other words, the DOS is at least 1,preferably at least 2, 4, 5, 7, 9, or 10.

The term “interpolymer” is used herein to indicate, for example, acopolymer or a terpolymer. That is, at least one other comonomer ispolymerized with ethylene to make an interpolymer.

The molecular weight distribution, M_(w)/M_(n), of the composition ispreferably less than 20, more preferably less than or equal to 19, mostpreferably less than or equal to 18, especially less than or equal to17.5 and most especially in the range of from about 10 to about 17.5. Insome embodiments, the MWD of the overall composition is less than 10,such as about 5, about 7, or about 9. Alternatively, the composition ispreferably characterized as having an I_(21.6)/I₅ ratio of less than orequal to 22.5, more preferably less than or equal to 22, most preferablyless than or equal to 21 and especially less than or equal to 20.

The relatively narrow molecular weight distribution, bimodalpolyethylene composition is also characterized as having an overalldensity of greater than or equal to 0.94 g/cm³, preferably in the rangeof from about 0.94 to about 0.97 g/cm³, more preferably from about 0.948to about 0.968 g/cm³, and an I₅ melt index of less than or equal to 0.5g/10 min., preferably in the range of from about 0.01 to about 0.5 g/10minutes, more preferably from about 0.05 to about 0.45 g/10 minutes.

Alternatively, the novel composition can be characterized as havingM_(v1)/M_(v2) ratio of less than or equal to 0.8, preferably less thanor equal to 0.6, more preferably less than or equal to 0.4, where M_(v1)is the viscosity average molecular weight of the LMW high densitycomponent and M_(v2) is the viscosity average molecular weight of theHMW interpolymer component, as determined using ATREF-DV analysis asdescribed in detail in WO 99/14271, the disclosure of which isincorporated herein by reference. WO 99/14271 also describes a suitabledeconvolution technique for multicomponent polymer blend compositions.

In some embodiments, the novel composition is characterized by a lowductile to brittle transition temperature, T_(db). T_(db) may bemeasured by the S4 test and is sometimes referred to as the criticaltemperature for rapid crack propagation measurements. T_(db) may alsodetermined from critical strain energy release rate, G_(C), measurementsin the Charpy mode. Some novel compositions described herein have aT_(db) of less than about −20° C. Preferably, T_(db) is about −30° C. orless, or about −40° C. or less. More preferably, T_(db) is about −45° C.or less. In some embodiments, T_(db) is about −50° C. or about −60° C.or less.

Some novel compositions are also characterized by exceptional resistanceto slow crack growth as measured by the PENT test. Typically,compositions described herein have PENT lifetimes of about 110,000minutes or more at 2.4 MPa and 80° C. Preferably, compositions have PENTlifetimes of about 150,000 to about 200,000 minutes or more. Mostpreferably, compositions have a PENT lifetime of about 250,000 to about500,000 minutes.

Generally, the novel composition may comprise any amount of the LMWcomponent or the HMW component, i.e., either component can be presentfrom about 0.5 weight percent to about 99.5 percent. In someembodiments, the novel composition comprises from about 35 to about 65weight percent, preferably from about 45 to about 55 weight percent of alow molecular weight (LMW) high density ethylene homopolymer component.The LMW component has an I₂ melt index of less than or equal to 2000g/10 minutes, preferably it is characterized as having an I₂ melt indexof from about 30 to about 2000 g/10 minutes, more preferably 40 to 1000g/10 min., most preferably from about 50 to about 150 g/10 minutes. TheM_(w) of the LMW component is preferably in the range from about 10,000to about 40,000 g/mole, more preferably in the range of from about25,000 to about 31,000 g/mole. The M_(w)/M_(n) of the LMW component ispreferably less than 8, more preferably less than 5, most preferablyabout 3 or less. In other embodiments the M_(w)/M_(n) of the LMWcomponent is about 2 or less. In some embodiments, the molecular weightdistribution, M_(w)/M_(n), of the LMW component is in the range of fromabout 1.5 to about 4.8. In certain embodiments, the M_(w)/M_(n) of theLMW component is most preferably in the range of from about 3.2 to about4.5. The density of the LMW component is preferably greater than 0.960g/cm³, more preferably greater than or equal to 0.965 g/cm³ and mostpreferably greater than or equal to 0.970 g/cm³.

The novel composition comprises from about 65 to about 35 weightpercent, more preferably from about 55 to about 45 weight percent of ahigh molecular weight (HMW) ethylene interpolymer component. The HMWinterpolymer component has an I₂ melt index of less than or equal to 0.1g/10 minutes, preferably it is characterized as having an I₂ melt indexof from about 0.001 to about 0.1 g/10 minutes, more preferably fromabout 0.005 to about 0.05 g/10 minutes, most preferably from about0.0085 to about 0.016. The HMW component is also characterized by itsI_(21.6) melt index ranging from about 0.1 to about 1.0 g/10 min. Insome embodiments, I_(21.6) preferably ranges from about 0.1 to about 0.6g/10 min., preferably from about 0.1 to about 0.5 g/10 min., morepreferably from about 0.3 to about 0.4 g/10 min. In other embodiments,I_(21.6) ranges from greater than 0.6 to about 1.0 g/10 min., preferablyfrom about 0.65 to about 0.95 g/10 min., more preferably from about 0.7to about 0.9 g/10 min.

The M_(w) of the HMW component is preferably in the range from about100,000 to about 600,000 g/mole, more preferably in the range of fromabout 300,000 to about 500,000 g/mole, and most preferably in the rangeof from about 375,000 to about 450,000 g/mole. The molecular weightdistribution of the HMW component, MWD^(H), may be broad, but istypically less than about 8. In some embodiments, MWD^(H) is less thanabout 5. Some preferred embodiments have a HMW component with a MWD^(H)of about 3 or less, more preferably about 2 or less.

Preferably, the HMW component has a density ranging from about 0.905 toabout 0.955 g/cm³. In some embodiments a lower limit of the preferreddensity range is about 0.910 or about 0.915 g/cm³ or about 0.920 g/cm³.In some embodiments, an upper limit for the density of the HMW componentmay be about 0.950 g/cm³, about 0.940 g/cm³, or about 0.930 g/cm³.

Preferably, the MWD of each component is unimodal and more preferablyunimodal and distinct. Preferably, the ratio of the molecular weights ofthe HMW component and the LMW component, M_(w) ^(H)/M_(w) ^(L), is about1.3 or higher.

In some embodiments, the M_(w)/M_(n) of the HMW component is relativelynarrow. That is, preferably the M_(w)/M_(n) of the HMW component is lessthan 4.8, more preferably less than or equal to 4.5, most preferably inthe range of from about 1.5 to about 4, and especially in the range offrom about 2.7 to about 3.1. The density of the HMW component is lessthan or equal to about 0.949 g/cm³, preferably less than or equal toabout 0.945 g/cm³ and more preferably in the range of from about 0.92 toabout 0.943 g/cm³.

In other embodiments, the HMW interpolymer component is a homogeneouspolymer or is characterized as having a substantially uniform comonomerdistribution. Information regarding the relative uniformity of thecomonomer distribution for ethylene interpolymers is typically describedby the SCBDI (Short Chain Branch Distribution Index) or CDBI(Composition Distribution Branch Index), which are used interchangeablyherein. SCBDI is defined as the weight percent of the polymer moleculeshaving a comonomer content within 50 percent of the median total molarcomonomer content and represents a comparison of the comonomerdistribution in the interpolymer to the comonomer distribution expectedfor a Bernoullian distribution. The SCBDI of an interpolymer can bereadily calculated from TREF as described, for example, by Wild et al.,Journal of Polymer Science, Poly. Phys. Ed., Vol. 20, p. 441 (1982);U.S. Pat. No. 4,798,081; U.S. Pat. No. 5,008,204; or L. D. Cady, “TheRole of Comonomer Type and Distribution in LLDPE Product Performance,”SPE Regional Technical Conference, Quaker Square Hilton, Akron, Ohio,October 1-2, pp. 107-119 (1985), the disclosures of all four of whichare incorporated herein by reference.

The preferred TREF technique does not include purge quantities in SCBDIcalculations. More preferably, the comonomer distribution of theinterpolymer and SCBDI are determined using ¹³C NMR analysis inaccordance with techniques described in U.S. Pat. No. 5,292,845; U.S.Pat. No. 4,798,081; U.S. Pat. No. 5,089,321 and by J. C. Randall, Rev.Macromol. Chem. Phys., C29, pp. 201-317, the disclosures of all four ofwhich are incorporated herein by reference.

In analytical temperature rising elution fractionation analysis (asdescribed in U.S. Pat. No. 4,798,081 and abbreviated herein as “ATREF”),the composition to be analyzed is dissolved in a suitable hot solvent(for example, trichlorobenzene) and allowed to crystallized in a columncontaining an inert support (stainless steel shot) by slowly reducingthe temperature. The column is equipped with both a refractive indexdetector and a differential viscometer (DV) detector. An ATREF-DVchromatogram curve is then generated by eluting the crystallized polymersample from the column by slowly increasing the temperature of theeluting solvent (trichlorobenzene). The ATREF curve is also frequentlycalled the short chain branching distribution (SCBD), since it indicateshow evenly the comonomer (for example, octene) is distributed throughoutthe sample in that as elution temperature decreases, comonomer contentincreases. The refractive index detector provides the short chaindistribution information and the differential viscometer detectorprovides an estimate of the viscosity average molecular weight. Theshort chain branching distribution and other compositional informationcan also be determined using crystallization analysis fractionation suchas the CRYSTAF fractionalysis package available commercially fromPolymerChar, Valencia, Spain.

Accordingly, when the comonomer distribution of the interpolymercomponent is substantially uniform, it has a SCBDI of greater than 50percent, especially greater than 70 percent, and most especially greaterthan about 90, 95, or 99 percent. SCBDI determination clearlydistinguishes such polymers from very low density polyethylenes (VLDPEs)which generally have a broad composition distribution as assessed bySCBDI values that are generally less than about 55 percent.

Preferably, the homogeneous copolymers exhibit an essentially singularmelting point characteristic, with a peak melting point (T_(m)), asdetermined by Differential Scanning Calorimetry (DSC), of from about 60°C. to about 110° C. Preferably the homogeneous copolymer has a DSC peakT_(m) of from about 80° C. to about 100° C. As used herein, the phrase“essentially single melting point” means that at least about 80 percent,by weight, of the material corresponds to a single T_(m) peak at atemperature within the range of from about 60° C. to about 110° C., andessentially no substantial fraction of the material has a peak meltingpoint in excess of about 115° C., as determined by DSC analysis. DSCmeasurements are made on a Perkin Elmer System 7 Thermal AnalysisSystem. Melting information reported are second melting data, i.e., thesample is heated at a programmed rate of 10° C./min. to a temperaturebelow its critical range. The sample is then reheated (2nd melting) at aprogrammed rate of 10° C./min. The presence of higher melting peaks isdetrimental to film properties such as haze, and compromises the chancesfor meaningful reduction in the seal initiation temperature of the finalfilm.

Processes for preparing homogeneous polymers are disclosed in U.S. Pat.No. 5,206,075, U.S. Pat. No. 5,241,031, and PCT InternationalApplication WO 93/03093, each of which is hereby incorporated byreference thereto in its entirety. Further details regarding theproduction and use of one genus of homogeneous ethylene α-olefincopolymers are disclosed in U.S. Pat. No. 5,206,075, to Hodgson, Jr.;U.S. Pat. No. 5,241,031, to Mehta; PCT International Publication NumberWO 93/03093, in the name of Exxon Chemical Company; PCT InternationalPublication Number WO 90/03414, in the name of Exxon Chemical Patents,Inc., all four of which are hereby incorporated in their entireties, byreference there. Still another genus of homogeneous ethylene/α-olefincopolymers is disclosed in U.S. Pat. No. 5,272,236, to Lai, et. al., andU.S. Pat. No. 5,278,272, to Lai, et. al., both of which are herebyincorporated in their entireties, by reference thereto.

Homogeneously branched linear ethylene/α-olefin interpolymers may alsobe prepared using polymerization processes (for example, as described byElston in U.S. Pat. No. 3,645,992) which provide a homogeneous shortchain branching distribution. In his polymerization process, Elston usessoluble vanadium catalyst systems to make such polymers. However, otherssuch as Mitsui Petrochemical Company and Exxon Chemical Company haveused so-called single site catalyst systems to make polymers having ahomogeneous linear structure. U.S. Pat. No. 4,937,299 to Ewen et al. andU.S. Pat. No. 5,218,071, to Tsutsui et al. disclose the use of catalystsystems based on hafnium for the preparation of homogeneous linearethylene polymers. Homogeneous linear ethylene/α-olefin interpolymersare currently available from Mitsui Petrochemical Company under thetrade name “Tafmer” and from Exxon Chemical Company under the trade name“Exact”.

Substantially linear ethylene/α-olefin interpolymers are available fromThe Dow Chemical Company as AFFINITY™ polyolefin plastomers.Substantially linear ethylene/α-olefin interpolymers may be prepared inaccordance with the techniques described in U.S. Pat. No. 5,272,236,U.S. Pat. No. 5,278,272, and U.S. Pat. No. 5,665,800, which are herebyincorporated by reference.

Other suitable homogeneous ethylene/α-olefin polymers include ultra-lowmolecular weight polymers made in accordance with the teaching of U.S.Pat. No. 6,054,544, which is hereby incorporated in its entirety.

In yet other embodiments, the HMW ethylene interpolymer component, ischaracterized as having a reverse comonomer distribution such that ahigher amount of comonomer in the interpolymer component is incorporatedin the high molecular weight fractions of the interpolymer component.That is, the polymer fractions having a M_(w) greater than or equal tothe average M_(w) of the interpolymer component are characterized ashaving a higher weight average amount of comonomer than the polymerfractions having a M_(w) less than the average M_(w) of the interpolymercomponent. For example, in some embodiments, the total molar comonomercontent of all polymer fractions having a M_(w) greater than or equal to300,000 g/mole will be at least 25 percent higher, more preferably atleast 30 percent higher than the molar comonomer content of thosepolymer fractions having a Mw of less than or equal to 100,000 g/mole.

Reverse comonomer distribution may be quantified as follows. Withrespect to ethylene copolymer component, when, in cross fractionationchromatography (CFC) of the ethylene copolymer, with respect toextraction at an arbitrary temperature T (° C.) falling within the rangeof between a first temperature at which a maximum amount of extractionis exhibited and a second temperature which is the lower temperature ofeither the temperature of 10° C. higher than said first temperature of96° C., the relationship between the arbitrary temperature T (° C.) anda point in molecular weight on a molecular weight distribution profileof a copolymer fraction extracted at the arbitrary temperature T (° C.)at which point in molecular weight the molecular weight distributionprofile of the copolymer fraction shows a peak having a maximumintensity is treated by the least squares method to obtain anapproximate straight line within the range of between said firsttemperature and said second temperature; if there is the copolymerfraction the amount of which is less than 1% by weight on the totalamount, excluding purge, of copolymer fraction extracted at temperaturesin the overall range of extraction temperatures in CFC, the copolymerfraction can be excluded from the calculation for the approximatestraight line; the approximate straight line has a gradient within therange defined by the formula (I):

−1≦{log Mp(T ¹)−log Mp(T ²)}/(T ¹ −T ²)≦0.005  (I)

wherein:

T¹ and T² are two different arbitrary extraction temperatures T (° C.)within the range of between the first temperature and the secondtemperature and

Mp(T¹) and Mp(T²) are, respectively, molecular weights corresponding toT¹ and T² on said approximate straight line.

In the above formula (I), the term {log Mp(T¹)−log Mp(T²)}/(T¹−T²)indicates a gradient of the above-mentioned approximate straight line.

In some embodiments, the cross fraction chromatography (CFC) isconducted using CFC T-150A (manufactured and sold by Mitsubishi KagakuCorp., Japan). The measurement by CFC is conducted as follows: 20 mg ofa sample is dissolved in 20 ml of dichlorobenzene having a temperatureof 140° C., to thereby obtain a solution of the sample. Then, 5 ml ofthe obtained solution is added to a TREF (temperature rising elutionfractionation) column filled with glass beads, and the solution isallowed to cool to 0° C. at a rate of 1° C./min. Subsequently, thesolution is heated, so as to elevate the temperature of the solution ata rate of 1° C./min, thereby extracting copolymer fractions. Then, theextracted copolymer fractions are subjected to gel permeationchromatography (GPC) using a GPC column Shodex AD806MS (manufactured andsold by Showa Denko K.K., Japan), followed by Fourier transformationinfrared spectroscopy (FT-IR) using Nicolet Magna-IR spectrometer 550(manufactured and sold by Nicolet Co., Ltd., U.S.A.).

With respect to conventional ethylene copolymers produced using aconventional Ziegler catalyst, the gradient{logMp(T¹)−logMp(T²)}/(T¹−T²) is generally a positive value. Withrespect to conventional ethylene copolymers produced using conventionalmetallocene catalysts which have recently been being put into practicaluse, the gradient {log Mp(T¹)−log Mp(T²)}/(T¹−T²) is almost 0, thus theyhave a substantially uniform comonomer distribution.

The ethylene copolymer component in some embodiments of the inventionhas a gradient [{log Mp(T¹)−log Mp(T²)}/(T¹−T²)] which is relativelylarge in negative value (within the range of from −0.005 to −1). Thisindicates that the copolymer has a reverse comonomer distribution. Inother words, in the ethylene copolymer component, a copolymer fractionhaving a high comonomer content has a high molecular weight, contrary tothe conventional ethylene copolymers, in which a copolymer fractionhaving a high comonomer content typically has a low molecular weight.

In some embodiments, the gradient should be preferably within theranges:

−0.5≦{log Mp(T ¹)−log Mp(T ²)}/(T ¹ −T ²)≦0.007;

or,

−0.1≦{log Mp(T ¹)−log Mp(T ²)}/(T ¹ −T ²)≦0.01;

or

−0.08≦{log Mp(T ¹)−log Mp(T ²)}/(T ¹ −T ²)≦0.02;

wherein T¹, T², Mp(T¹) and Mp(T²) are as defined for the formula (I).

In other embodiments, with respect to the ethylene copolymer component,the amount of such copolymer fractions extracted at temperatures whichare at least 10° C. lower than the first temperature as defined aboveare relatively small. Specifically, when the ethylene copolymercomponent is measured by CFC, the ethylene copolymer showscharacteristics such that the sum of respective amounts of copolymerfractions extracted at temperatures which are at least 10° C. lower thanthe first temperature as defined above is 8% by weight or less,preferably 5% by weight or less, more preferably 3.5% by weight or less,based on the total amount of copolymer fractions extracted attemperatures in the overall range of extraction temperatures in CFC, butexcluding the purge.

In some embodiments, certain fractions of the ethylene copolymercomponent satisfy the following formula (II):

log(Mt)−log(Mc)≦0.5  (II)

wherein Mt is a point in molecular weight on a molecular weightdistribution profile at which the profile shows a peak having a maximumintensity, and Mc is an arbitrary point in molecular weight on themolecular weight distribution profile.

The molecular weight distribution profile is obtained together with acomonomer content distribution profile by subjecting the ethylenecopolymer to gel permeation chromatography-Fourier transformationinfrared spectroscopy (GPC/FT-IR). An approximate straight line isobtained from the comonomer content distribution profile by the leastsquares method. The line has a gradient (hereinafter “comonomerdistribution gradient”) defined by the formula (III):

{C(Mc ¹)−C(Mc ²)}/(log Mc ¹−log Mc ²)  (III)

wherein:

Mc¹ and Mc² are two different arbitrary points (Mc) in molecular weightwhich satisfy the formula (II), and

C(Mc¹) and C(Mc²) are, respectively, comonomer contents corresponding toMc¹ and Mc² on the approximate straight line.

The comonomer distribution gradient, as defined as Formula (III), mayrange from about 0.0001 to about 0.1, about 0.0005 to about 0.05, orabout 0.001 to about 0.02, although other values outside the ranges arealso possible.

As mentioned above, the molecular weight distribution profile and thecomonomer content distribution profile can be obtained by subjecting theethylene copolymer to gel permeation chromatography/Fouriertransformation infrared spectroscopy (GPC/FT-IR). For example, themeasurement by GPC is conducted using 150C ALC/GPC (manufactured andsold by Waters Assoc. Co. U.S.A.), in which three columns [one ShodexAt-807S (manufactured and sold by Showa Denko K.K., Japan) and twoTSK-gel GMH-H6 (manufactured and sold by Tosoh Corp., Japan)], which areconnected in series, are used, and the measurement by FT-IR is connectedby dissolving 20 to 30 mg of a sample in 15 ml of trichlorobenzenehaving a temperature of 140° C., and applying 500 to 1,000 μl of theresultant solution to a FT-IR apparatus (PERKIN-ELMER 1760X,manufactured and sold by Perkin Elmer Cetus, Co., Ltd., U.S.A.).

As used herein, “comononer content” is defined as a value obtained bydividing the number of comonomer units relative to 1,000 methylene unitscontained in the copolymer by 1,000. For example, when 5 copolymer unitsare contained relative to 1,000 methylene units, the comonomer contentis 0.005. The value of the comonomer content can be obtained from theratio of the intensity of an absorbance attributed to the comonomerunits to the intensity of an absorbance attributed to the methyleneunits, which ratio can be obtained by FT-IR. For examle, when a linearα-olefin is used as a comonomer, the ratio of the intensity ofabsorbance at 2,960 cm−1, which is attributed to the methyl groups, tothe intensity of absorbance at 2,925 cm−1, which is attributed to themethylene groups, is obtained by FT-IR. From the obtained ratio, thecomonomer content can be obtained. The reverse comonomer distributioncharacteristic as well as cross-fractionation analysis are described inmore detail in WO 97/43323, the disclosure of which is incorporatedherein by reference.

The novel composition can be made by a variety of methods. For example,it may be made by blending or mixing a LMW high density homopolyethylenecomponent and a HMW ethylene copolymer component. Alternatively, it maybe made in a plurality of polymerization reactors.

In some embodiments, the composition is manufactured using at least onemetallocene catalyst system either alone or in combination with othermetallocene catalyst or a Ziegler-Natta catalyst. Preferably, to ensurethe HMW component is characterized as having a reverse comonomerdistribution, the metallocene or single-site catalyst system is aconstrained geometry catalyst system as descried in WO 96/16092 WO98/27119, and WO 96/28480, the disclosures of which are incorporatedherein by reference. In a preferred embodiment of the invention, thenovel composition is manufactured using multiple reactors in series orparallel with a metallocene catalyst being fed to each reactor or tojust the first reactor. In another preferred embodiment, the samemetallocene catalyst system is separately fed into twoindependently-controlled continuously stirred autoclave slurry reactors(CSTR) configured sequentially.

Preferably, the single-site or metallocene catalyst is supported usingan inert material such as silica. More preferably, even where scavengersare used, the single-site or metallocene catalyst is reacted with asuitable co-catalyst (e.g., a boron-containing compound or an alumoxane)which is bonded or fixed to the support in a prior step such that thesingle-site or metallocene catalyst is immobilized to the extent thatsubstantially no soluble catalyst species is extracted from the supportduring polymerization, most preferably the species are fixed or bondedsuch that there is substantially no extraction when the solid catalystsystem is boiled in toluene for 2 hours. Suitable single-site catalystsystems for use in manufacturing the novel composition are alsodescribed in detail in U.S. Pat. Nos. 6,043,180 and 5,834,393, thedisclosures of which are incorporated herein by reference.

While any known polymerization process is thought to be suitable for usein manufacturing the composition, preferably the novel composition ismanufactured using a particle-forming polymerization process (that is, aslurry or a gas phase process), more preferably using a slurrypolymerization process and most preferably using a slurry loop or slurryautoclave (CSTR) polymerization process comprised of at least tworeactors operated sequentially (i.e. in series). Most especially, a dualautoclave sequential polymerization system is used. In a preferredembodiment of the invention, the sequential polymerization is conductedsuch that fresh catalyst is separately injected in each reactor.Preferably, where separate catalyst injection into each reactor is, no(or substantially no) live polymer or active catalyst is carried overfrom the first reactor into the second reactor as the polymerization inthe second reactor is accomplished only from the injection of a freshcatalyst and monomer (and comonomer) thereto.

In another preferred embodiment, the composition is manufactured using amultiple reactor system (preferably a two reactor system) in series withfresh catalyst feed injection of a supported catalyst system into thefirst reactor only with process adjustments being made such that livepolymer and/or catalyst species is carried over from the first reactorto a subsequent reactor to effect polymerization with fresh monomer andoptionally comonomer.

Most preferably, whether separate injection into each reactor is used orinjection into the first reactor is used, the resulting composition ischaracterized as comprising component polymers having distinct, unimodalmolecular weight distributions.

For multiple reactor polymerizations, a pressure control device (e.g., astripper, extrusion valve and/or pump) may be employed in the flowstream between sequential reactors. The above processes are disclosed inU.S. Provisional Patent Application Serial No. 60/313,176, filed Aug.17, 2001, entitled “Particle-Form Ethylene Polymerization Process,” inthe names of Ruddy A. J. Nicasy, et al., which is incorporated byreference herein in its entirety.

In the sequential polymerization, the LMW high density component or theHMW interpolymer component may be manufactured in the first reactor. Butdue to process control consideration, the HMW component is preferablymade in the first reactor.

In addition to sequential polymerization, the novel composition can alsobe manufactured from single-reactor or multi-reactor component polymersusing dry, tumble or extrusion blending techniques.

The HMW interpolymer component comprises ethylene with at least oneolefin, preferably a C₃-C₂₀ α-olefin or C₄-C₁₈ diolefin. Suitablecomonomers include, but are not limited to, the C₃-C₂₀ α-olefin, such aspropylene, isobutylene, 1-butene, 1-hexene, 4-methyl-1-pentene,1-heptene, 1-octene, 1-nonene, and 1-decene. In some embodiments, theHMW interpolymer component is a copolymer of ethylene and 1-butene.Chain transfer agents can also be used in the polymerization.

Density is measured in accordance with ASTM D-792. Melt indexmeasurements are performed according to ASTM D-1238, Condition 190°C./2.16 kilogram (kg) and Condition 190° C./5 kg, and are known as I₂and I₅, respectively. Melt index is inversely proportional to themolecular weight of the polymer. Thus, the higher the molecular weight,the lower the melt index, although the relationship is not linear. Meltindex is reported as g/10 minutes. Melt index determinations can also beperformed with even higher weights, such as in accordance with ASTMD-1238, Condition 190° C./10 kg and Condition 190° C./21.6 kg, and areknown as I₁₀ and I_(21.6), respectively.

The term “melt flow ratio” is used herein in the conventional sense asthe ratio of a higher weight melt index determination to a lower weightdetermination. For measured I₁₀ and I₂ melt index values, the melt flowratio is conveniently designated as I₁₀/I₂. For I_(21.6) and I₁₀ 651values, the ratio is designated I_(21.6)/I₁₀.

Gel Permeation Chromatography (GPC) data were generated using either aWaters 150C/ALC, a Polymer Laboratories Model PL-210 or a PolymerLaboratories Model PL-220. The column and carousel compartments wereoperated at 140° C. The columns used were 3 Polymer Laboratories 10micron Mixed-B columns. The samples were prepared at a concentration of0.1 grams of polymer in 50 milliliters of 1,2,4 trichlorobenzene. The1,2,4 trichlorobenzene used to prepare the samples contained 200 ppm ofbutylated hydroxytoluene (BHT). Samples were prepared by agitatinglightly for 2 hours at 160° C. The injection volume used was 100microliters and the flow rate was 1.0 milliliters/minute. Calibration ofthe GPC was performed with narrow molecular weight distributionpolystyrene standards purchased from Polymer Laboratories. Thesepolystyrene standard peak molecular weights were converted topolyethylene molecular weights using the following equation (asdescribed in Williams and Ward, J. Polym. Sci., Polym. Let., 6, 621(1968):

M _(polyethylene) =A×(M _(polystyrene))^(B)

where M is the molecular weight, A has a value of 0.4316 and B is equalto 1.0. The molecular weight calculations were performed with theViscotek TriSEC software.

The GPC data were then deconvoluted to give the most probable fit fortwo molecular weight components. There are a number of deconvolutionalgorithms available both commercially and in the literature. These maylead to different answers depending upon the assumptions used. Thealgorithm summarized here is optimized for the deconvolution problem ofthe two most probable molecular weight distributions (plus an adjustableerror term). In order to allow for the variations in the underlyingdistributions due to the macromer incorporation and small fluctuationsin the reactor conditions (i.e., temperature, concentration) the basisfunctions were modified to incorporate a normal distribution term. Thisterm allows the basis function for each component to be “smeared” tovarying degrees along the molecular weight axis. The advantage is thatin the limit (low LCB, perfect concentration and temperature control)the basis function will become a simple, most probable, Florydistribution.

Three components (j=1,2,3) are derived with the third component (j=3)being an adjustable error term. The GPC data must be normalized andproperly transformed into weight fraction versus Log₁₀ molecular weightvectors. In other words, each potential curve for deconvolution shouldconsist of a height vector, h_(i), where the heights are reported atknown intervals of Log₁₀ molecular weight, the h_(i) have been properlytransformed from the elution volume domain to the Log₁₀ molecular weightdomain, and the h_(i) are normalized. Additionally, these data should bemade available for the EXCEL application.

Several assumption are made in the deconvolution. Each component, j,consists of a most probable, Flory, distribution which has beenconvoluted with a normal or Gaussian spreading function using aparameter, μ_(j). The resulting, three basis functions are used in aChi-square, μ², minimization routine to locate the parameters that bestfit the n points in h₁, the GPC data vector.${{X^{2}\left( {\mu_{j},\sigma_{j},w_{j}} \right)} = {\sum\limits_{i = 1}^{n}\left\lbrack {{\sum\limits_{j = 1}^{3}{\cdot {\sum\limits_{k = 1}^{20}{{w_{j}\quad \cdot M_{i}^{2} \cdot \lambda_{j,k}^{2} \cdot {CumND}_{j,k} \cdot e^{{- \lambda_{j,k}} \cdot M_{1}} \cdot \Delta}\quad {Log}_{10}M}}}} - h_{i}} \right\rbrack^{2}}}\quad$$\quad {\lambda_{j,k} = {10^{\mu_{j} + {\frac{k - 10}{3} \cdot \sigma_{j}}}{\quad {\quad }}}}$

The variable, CumND_(j,k), is calculated using the EXCEL* function“NORMDIST(x, mean, standard_dev, cumulative)” with the parameters set asfollows:

x=μ_(j)+(k−10)*μμ_(j)/3

mean=μ_(j)

standard dev=μ_(j)

cumulative=TRUE

Table 1 below summarizes these variables and their definitions. The useof the Microsoft® EXCEL software application, Solver, is adequate forthis task. Constraints are added to Solver insure proper minimization.

TABLE 1 Variable Definitions Variable Name Definition μ_(j,k) Reciprocalof the number average molecular weight of most probable (Flory)distribution for component j, normal distribution slice k μ_(j) Sigma(square root of variance) for normal (Gaussian) spreading function forcomponent j. W_(j) Weight fraction of component j K Normalization term(1.0/Log_(e) 10) M_(i) Molecular weight at elution volume slice i h_(i)Height of log₁₀ (molecular weight) plot at slice i n Number of slices inLog molecular weight plot i Log molecular weight slice index (1 to n) jComponent index (1 to 3) l. k Normal distribution slice index μlog₁₀MAverage difference between log₁₀M_(i) and log₁₀M_(i−1) in height vs.log₁₀M plot

The 8 parameters that are derived from the Chi-square minimization areμ1, μ2, μμ3, μ1, μ2, μμ3, w1, and w2. The term w3 is subsequentlyderived from w1 and w2 since the sum of the 3 components must equal 1.Table 2 is a summary of the Solver constraints used in the EXCELprogram.

TABLE 2 Constraint summary Description Constraint Maximum of fraction 1w₁ < 0.95 (User adjustable) Lower limit of spreading μ₁, μμ₂, μμ₃ >0.001 (must be positive) function Upper limit of spreading μ₁, μμ₂, μμ₃< 0.2 (User adjustable) function Normalized fractions w₁ + w₂ + w₃ = 1.0

Additional constraints that are to be understood include the limitationthat only μ_(j)>0 are allowed, although if solver is properlyinitialized, this constraint need not be entered, as the solver routinewill not move any of the μ_(j) to values less than about 0.005. Also,the w_(j) are all understood to be positive. This constraint can behandled outside of solver. If the w_(j) are understood to arise from theselection of two points along the interval 0.0<P₁<P₂<1.0; whereby w₁=P₁,w₂=P₂−P₁ and w₃=1.0−P₂; then constraining P1 and P2 are equivalent tothe constraints required above for the w_(j).

Table 3 is a summary of the Solver settings under the Options tab.

TABLE 3 Solver settings Label Value or selection Max Time (seconds) 1000Iterations 100 Precision 0.000001 Tolerance (%) 5 Convergence 0.001Estimates Tangent Derivatives Forward Search Newton ALL OTHER SELECTIONSNot selected

A first guess for the values of μ₁, μ₂, w₁, and w₂ can be obtained byassuming two ideal Flory components that give the observed weightaverage, number average, and z-average molecular weights for theobserved GPC distribution. $\begin{matrix}{M_{n,{GPC}} = \left\lbrack {{w_{1} \cdot \frac{1}{10^{\mu_{1}}}} + {w_{2} \cdot \frac{1}{10^{\mu_{2}}}}} \right\rbrack^{- 1}} \\{M_{w,{GPC}} = \frac{\left\lbrack {{w_{1} \cdot 2 \cdot 10^{\mu_{1}}} + {w_{2} \cdot 2 \cdot 10^{\mu_{2}}}} \right\rbrack}{M_{n,{GPC}}}} \\{{M_{z,{GPC}} = \frac{\left\lbrack {{w_{1} \cdot 6 \cdot 10^{\mu_{1}}} + {w_{2} \cdot 6 \cdot 10^{\mu_{2}}}} \right\rbrack}{M_{w,{GPC}}}}{{w_{1} + w_{2}} = 1}}\end{matrix}$

The values of μ1, μ2, w1, and w2 are then calculated. These should beadjusted carefully to allow for a small error term, w3, and to meet theconstraints in Table 2 before entering into Solver for the minimizationstep. Starting values for μj are all set to 0.05.

Preparative GPC for collecting selected fractions of polymers wasperformed on a Waters 150C/ALC equipped with preparative pump heads andmodified with a 3000 microliter injection loop and 14 milliliter samplevials. The column and carousel compartments were operated at 140° C. Thepreparative GPC column used was 1 Jordi Associaties 5 microndivinylbenzene (DVB) column catalog number 15105. The column dimensionswere 500 mm in length and 22 mm inner diameter. 1,2,4 trichlorobenzenewas used for both sample preparation and as the chromatographic mobilephase. The samples were prepared at a concentration of 0.1 grams ofpolymer in 50 milliliters of solvent. The solvent used to prepare thesamples contained 200 ppm of butylated hydroxytoluene (BHT). Sampleswere prepared by agitating lightly for 2 hours at 160° C. The injectionvolume used was 2,500 microliters and the flow rate was 5.0milliliters/minute.

Approximately 200-300 injections were made to collect appropriate sampleamounts for off-line analysis. 16 fractions were collected spanning thefull column elution range, with 8-12 fractions typically spanning thesample elution range. Elution range was verified by refractive indexanalysis during start-up. The collected solvent fractions wereevaporated to approximately 50-60 milliliter volumes with a BuchiRotovapor R-205 unit equipped with a vacuum controller module V-805 anda heating bath module B-409. The fractions were then allowed to cool toroom temperature and the polyethylene material was precipitated byadding approximately 200 milliliters of methanol. Verification ofmolecular weight fractionation was done via high temperature GPCanalysis with refractive index detection. Typical polydispersities ofthe fractions as measured by GPC analysis were approximately 1.1 to 1.4.

The weight average branching index for selected fractions was obtainedfrom direct determination of intrinsic viscosity and molecular weight ateach chromatographic data slice. The chromatographic system consisted ofeither a Polymer Laboratories Model PL-210 or a Polymer LaboratoriesModel PL-220 equipped with a Viscotek differential viscometer Model210R, and a Precision Detectors 2-angle laser light scattering detectorModel 2040. The 15-degree angle of the light scattering detector wasused for the calculation of molecular weights.

The column and carousel compartments were operated at 140° C. Thecolumns used were 3 Polymer Laboratories 10-micron Mixed-B columns. Thesolvent used was 1,2,4 trichlorobenzene. The samples were prepared at aconcentration of 0.1 grams of polymer in 50 milliliters of solvent. Thesolvent used to prepare the samples contained 200 ppm of butylatedhydroxytoluene (BHT). Samples were prepared by agitating lightly for 2hours at 160° C. The injection volume used was 100 microliters and theflow rate was 1.0 milliliters/minute.

Calibration of the GPC column set was performed with narrow molecularweight distribution polystyrene standards purchased from PolymerLaboratories. The calibration of the detectors was performed in a mannertraceable to NBS 1475 using a linear polyethylene homopolymer. 13C NMRwas used to verify the linearity and composition of the homopolymerstandard. The refractometer was calibrated for mass verificationpurposes based on the known concentration and injection volume. Theviscometer was calibrated with NBS 1475 using a value of 1.01deciliters/gram and the light scattering detector was calibrated usingNBS 1475 using a molecular weight of 52,000 Daltons.

The Systematic Approach for the determination of multi-detector offsetswas done in a manner consistent with that published by Mourey and Balke,Chromatography of Polymers: T. Provder, Ed.; ACS Symposium Series 521;American Chemical Society: Washington, D.C., (1993) pp 180-198 andBalke, et al.; T. Provder, Ed.; ACS Symposium Series 521; AmericanChemical Society: Washington, D.C., (1993): pp 199-219, both of whichare incorporated herein by reference in their entirety. The tripledetector results were compared with polystyrene standard referencematerial NBS 706 (National Bureau of Standards), or DOW chemicalpolystyrene resin 1683 to the polystyrene column calibration resultsfrom the polystyrene narrow standards calibration curve.

Verification of detector alignment and calibration was made by analyzinga linear polyethylene homopolymer with a polydispersity of approximately3 and a molecular weight of 115,000. The slope of the resultantMark-Houwink plot of the linear homopolymer was verified to be withinthe range of 0.725 to 0.730 between 30,000 and 600,000 molecular weight.The verification procedure included analyzing a minimum of 3 injectionsto ensure reliability. The polystyrene standard peak molecular weightswere converted to polyethylene molecular weights using the method ofWilliams and Ward described previously. The agreement for Mw and Mnbetween the polystyrene calibration method and the absolute tripledetector method were verified to be within 5% for the polyethylenehomopolymer.

Cross fraction chromatography (CFC) is conducted using CFC T-150A(manufactured and sold by Mitsubishi Kagaku Corp., Japan) as follows: 20mg of a sample is dissolved in 20 ml of dichlorobenzene having atemperature of 140° C., to thereby obtain a solution of the sample.Then, 5 ml of the obtained solution is added to a TREF (temperaturerising elution fractionation) column filled with glass beads, and thesolution is allowed to cool to 0° C. at a rate of 1° C./min.Subsequently, the solution is heated, so as to elevate the temperatureof the solution at a rate of 1° C./min, thereby extracting copolymerfractions. Then, the extracted copolymer fractions are subjected to gelpermeation chromatography (GPC) using a GPC column Shodex AD806MS(manufactured and sold by Showa Denko K.K., Japan), followed by Fouriertransformation infrared spectroscopy (FT-IR) using a Nicolet Manga-IRspectrometer 550 (manufactured and sold by Nicolet Co., Ltd., USA).Further details of CFC analysis can be found in the catalogue attachedto the above-mentioned CFC T-150A. The tensile properties were measuredin accordance with ASTM D 638-76.

Fabricated Articles Made From the Novel Compositions

The novel composition is particularly useful in fabricating blow moldedarticles (especially those characterized as having high toploadperformance) and transmission or distribution pipes for water and gases,especially pipes that substantially exceed a PE100 performance rating.In other words, the novel composition can be used to increase theservice life of the pipe. U.S. Pat. Nos. 6,204,349; 6,191,227;5,908,679; 5,683,767; 5,417,561, and 5,290,498 disclose various pipesand methods of making the pipes which can be used in embodiments of theinvention. As such, the disclosures of all of the preceding patents areincorporated by reference in their entirety.

Many useful fabricated articles can be made from the novel compositionsdisclosed herein. For example, molding operations can be used to formuseful fabricated articles or parts from the compositions disclosedherein, including various injection molding processes (e.g., thatdescribed in Modern Plastics Encyclopedia/89, Mid October 1988 Issue,Volume 65, Number 11, pp. 264-268, “Introduction to Injection Molding”by H. Randall Parker and on pp. 270-271, “Injection MoldingThermoplastics” by Michael W. Green, the disclosures of which areincorporated herein by reference) and blow molding processes (e.g., thatdescribed in Modern Plastics Encyclopedia/89, Mid October 1988 Issue,Volume 65, Number 11, pp. 217-218, “Extrusion-Blow Molding” byChristopher Irwin, the disclosure of which is incorporated herein byreference), profile extrusion, calandering, pultrusion (e.g., pipes) andthe like. Rotomolded articles can also benefit from the novelcompositions described herein. Rotomolding techniques are well known tothose skilled in the art and include, for example, those described inModern Plastics Encyclopedia/89, Mid October 1988 Issue, Volume 65,Number 11, pp. 296-301, “Rotational Molding” by R. L. Fair, thedisclosure of which is incorporated herein by reference).

Fibers (e.g., staple fibers, melt blown fibers or spunbonded fibers(using, e.g., systems as disclosed in U.S. Pat. Nos. 4,340,563,4,663,220, 4,668,566, or 4,322,027, all of which are incorporated hereinby reference), and gel spun fibers (e.g., the system disclosed in U.S.Pat. No. 4,413,110, incorporated herein by reference), both woven andnonwoven fabrics (e.g., spunlaced fabrics disclosed in U.S. Pat. No.3,485,706, incorporated herein by reference) or structures made fromsuch fibers (including, e.g., blends of these fibers with other fibers,e.g., PET or cotton)) can also be made from the novel compositionsdisclosed herein.

Film and film structures can also be made from the novel compositionsdescribed herein by using conventional hot blown film fabricationtechniques or other biaxial orientation processes such as tenter framesor double bubble processes. Conventional hot blown film processes aredescribed, for example, in The Encyclopedia of Chemical Technology,Kirk-Othmer, Third Edition, John Wiley & Sons, New York, 1981, Vol. 16,pp. 416-417 and Vol. 18, pp. 191-192, the disclosures of which areincorporated herein by reference. Biaxial orientation film manufacturingprocess such as described in a “double bubble” process as in U.S. Pat.No. 3,456,044 (Pahlke), and the processes described in U.S. Pat. No.4,352,849 (Mueller), U.S. Pat. No. 4,597,920 (Golike), U.S. Pat. No.4,820,557 (Warren), U.S. Pat. No. 4,837,084 (Warren), U.S. Pat. No.4,865,902 (Golike et al.), U.S. Pat. No. 4,927,708 (Herran et al.), U.S.Pat. No. 4,952,451 (Mueller), U.S. Pat. No. 4,963,419 (Lustig et al.),and U.S. Pat. No. 5,059,481 (Lustig et al.), the disclosures of each ofwhich are incorporated herein by reference, can also be used to makefilm structures from the novel compositions described herein. The filmstructures can also be made as described in a tenter-frame technique,such as that used for oriented polypropylene.

Other multi-layer film manufacturing techniques for food packagingapplications are described in Packaging Foods With Plastics, by WilmerA. Jenkins and James P. Harrington (1991), pp. 19-27, and in“Coextrusion Basics” by Thomas I. Butler, Film Extrusion Manual:Process, Materials, Properties pp. 31-80 (published by TAPPI Press(1992)) the disclosures of which are incorporated herein by reference.

The films may be monolayer or multilayer films. The film made from thenovel compositions can also be coextruded with the other layer(s) or thefilm can be laminated onto another layer(s) in a secondary operation,such as that described in Packaging Foods With Plastics, by Wilmer A.Jenkins and James P. Harrington (1991) or that described in “CoextrusionFor Barrier Packaging” by W. J. Schrenk and C. R. Finch, Society ofPlastics Engineers RETEC Proceedings, Jun. 15-17 (1981), pp. 211-229,the disclosure of which is incorporated herein by reference. If amonolayer film is produced via tubular film (i.e., blown filmtechniques) or flat die (i.e., cast film) as described by K. R. Osbornand W. A. Jenkins in “Plastic Films, Technology and PackagingApplications” (Technomic Publishing Co., Inc. (1992)), the disclosure ofwhich is incorporated herein by reference, then the film must go throughan additional post-extrusion step of adhesive or extrusion lamination toother packaging material layers to form a multilayer structure. If thefilm is a coextrusion of two or more layers (also described by Osbornand Jenkins), the film may still be laminated to additional layers ofpackaging materials, depending on the other physical requirements of thefinal film. “Laminations Vs. Coextrusion” by D. Dumbleton (ConvertingMagazine (September 1992)), the disclosure of which is incorporatedherein by reference, also discusses lamination versus coextrusion.Monolayer and coextruded films can also go through other post extrusiontechniques, such as a biaxial orientation process.

Extrusion coating is yet another technique for producing multilayer filmstructures using the novel compositions described herein. The novelcompositions comprise at least one layer of the film structure. Similarto cast film, extrusion coating is a flat die technique. A sealant canbe extrusion coated onto a substrate either in the form of a monolayeror a coextruded extrudate.

Generally for a multilayer film structure, the novel compositionsdescribed herein comprise at least one layer of the total multilayerfilm structure. Other layers of the multilayer structure include but arenot limited to barrier layers, and/or tie layers, and/or structurallayers. Various materials can be used for these layers, with some ofthem being used as more than one layer in the same film structure. Someof these materials include: foil, nylon, ethylene/vinyl alcohol (EVOH)copolymers, polyvinylidene chloride (PVDC), polyethylene terephthalate(PET), oriented polypropylene (OPP), ethylene/vinyl acetate (EVA)copolymers, ethylene/acrylic acid (EAA) copolymers, ethylene/methacrylicacid (EMAA) copolymers, LLDPE, HDPE, LDPE, nylon, graft adhesivepolymers (e.g., maleic anhydride grafted polyethylene), and paper.Generally, the multilayer film structures comprise from 2 to about 7layers.

EXAMPLES

The following examples are presented to illustrate various embodimentsof the invention. They are not intended to be representative of allembodiments of the invention and should be not construed to limit thescope of the claimed invention as described here. All numbers describedherein are approximate values and may vary within their accuracy ranges.

Example 1 was produced using an immobilized supported borate constrainedgeometry catalyst system in a small pilot continuously stirred-tank(autoclave) slurry polymerization system comprised of two reactorsconfigured sequentially. The immobilized solid catalyst system wasprepared as follows: Silica gel (948 grade available fromGrace-Davidson) was dehydrated at an elevated temperature to a totalvolatiles content of ca. 3 wt. %. 24.71 kg of the resulting silica wasslurried in 130 liters of dry hexane and then treated with 30.88 kg of a1.21 M solution of triethylaluminum (TEA) in hexane. The slurry wasfiltered and washed with fresh, dry hexane (130 liters per wash) atambient temperature until the residual aluminum in the wash was <0.5mmol/L. The solids were then isolated by filtration and dried undervacuum (˜10 torr) at 60° C. to a residual solvent level of less than orequal to 1.0 wt. %. 1.5 moles of [NHMe(C18-22H37-45)2] [HOC6H₄B(C6F5)3],as 16.95 kg of a 10.1 wt. % solution in toluene, was diluted by additionof 9.61 liters (8.32 kg) toluene. This solution was allowed to agitatefor 10 minutes and then 1.65 moles of TEA, as 0.88 liters (0.76 kg), ofa 1.87 M solution of TEA in toluene was added and the resulting solutionallowed to mix for 15 minutes. Then the solid silica/TEA was added overapproximately 30 minutes. On completion of the addition, the impregnatedmaterial was allowed to mix for 60 minutes. With continuous agitation,195 liters (128.7 kg) of dry, fresh hexane at ambient was added to thesolid and the resulting slurry was allowed to agitate for 30 minutes.Then 1.2 moles of a constrained geometry catalyst,(C5Me4SiMe2NtBu)Ti(η4-1,3-pentadiene) (as 3.69 kg of a 0.223 M solutionin heptane), was added and the slurry was mixed for 2 hours. The solventwas removed from the slurry by filtration and the resulting solid washedfour times with dry, fresh hexane at ambient and dried under vacuum toprovide a free flowing powder.

This immobilized supported borate constrained geometry catalyst systemwas then charged to a bomb and fed to the catalyst feed vessels of thereactor system which separately injects fresh catalyst into eachreactor. In these vessels, the supported catalyst system was furtherdiluted with dry, fresh hexane.

The small pilot slurry dual reactors had a volume of 10 liter and wereoperated at a liquid level of about 70% (by volume) and agitated at 1000rpm using a Lightnin A310 mixing blade. The reactor temperature was keptconstant by jacket cooling and the melt index was controlled viahydrogen addition while density was controlled via comonomer additionwherein the comonomer was 1-butene in all cases. All feed streams werefed through dip pipe legs in the liquid phase to allow intimate mixing.The diluent was hexane.

Example 1 was provided from by melt-compounding two substantiallyequivalent pilot reactor runs, Example 1A and Example 1B.Melt-compounding of small yield runs was necessary to provide sufficientquantities for testing and fabrication of articles. The conditions usedto produce Example 1A and Example 1B are reported in Table 4a and Table4b. The first reactor was operated at 65° C. and the ethylene flow ratewas 900 gram/hour (consumed), the hydrogen flow rate was 3.55Nliter/hour in a hexane flow of 2500 g/hour. In order to maintain aconstant pressure of 12 bar, 30 micromole/h of Ti was added. In none ofthe cases was an unbonded cocatalyst added to avoid reactor fouling andno (or a trace amount of) comonomer was added in order to prepare highdensity polyethylene in the first slurry stirred-tank reactor.

The total contents of the first reactor were continuously dumped intothe second slurry stirred-tank reactor which was operated at 75° C.wherein new feed streams were added: 750 g/h ethylene (consumed), nohydrogen flow, and 15 g/h 1-butene in 2500 g/h hexane. The secondreactor was operated at a slightly lower pressure (11 bar) to allowdumping from the first into the second reactor. Part of the gas phase ofthe second reactor was vented in order to control the hydrogenconcentration in the liquid phase. Additional catalyst feed was fed tothe second reactor to provide a relative production of 48.3% in thefirst reactor and 51.7% in the second reactor. The relative productionper reactor is referred to herein as “split” expressed as a percent orfractionally.

For selected runs, the gas phases in the two reactors were analyzed andthe results thereof are reported in Table 5. The contents of the secondreactor were continuously transferred to a flash tank operated at apressure of 1.3 bar and a temperature of 75° C., where the diluent andunreacted monomer and comonomer were flashed off. Flashing resulted in adry powder. The yields and product properties of Example 1A and Example1B are provided in Table 6.

Inventive Example 1 was prepared by melt-compounding Examples 1A and 1Bwith 750 ppm calcium stearate and 3000 ppm Irganox™ B225 on a LEISTRITZZSE 60 counter-rotating twin screw extruder. Included in themelt-compounding was a carbon black masterbatch based on DOWLEX™ LLDPE2384 resin to provide a final carbon black concentration of 2.28 weightpercent. The melt-compounding was mild in that the extruder (65 mm, L/D24) was operated using a temperature profile of 190 to 220° C. at 28kg/hr and 40 rpm. Inventive Example 1 was fed to achieve a minimalspecific energy and the atmosphere on the powder feeder was controlledto be 1-4% oxygen by using a nitrogen purge in the feeding chute.Inventive Example 1 was extruded two times to ensure good homogeneity.Final product properties for Inventive Example 1 can be found in Table4. Its I₅ melt index was 0.27 g/10 minutes and its density was 0.9668g/cm³.

As described in Tables 4-7, Inventive Example 2 was produced in a mannersimilar to Inventive Example 1, except Inventive Example 2 did notrequire blending of duplicative runs to increase available quantities.Inventive Example 2 was stabilized and compounded with carbon black inmanner similar to Inventive Example 1 and, as described in Table 7, hadan I₅ melt index of 0.20 g/10 minutes and a density of 0.9604 g/cm³.

TABLE 4a Process Conditions for First Reactor Reactor Reactor CatalystCocatalyst C₂ C₂ C₂ H₂ C₄ C₆ Stirrer Ex- Temp. Pressure Flow Flow FlowVented Consumed Flow Flow Flow Speed ample ° C. Bar μmol/h g/h g/h g/hg/h g/h g/h g/h rpm 1a 65 12 30 None 900 200 700 3.55 0 2500 1000 1b 6512 30 None 800 200 600 3.55 0 2500 1000 2  65 12 13.55 None 880 200 6803.7 0 2500 750 3a 65 11 32.8 None 900 200 700 3.55 0 2500 1000 3b 65 1124 None 920 200 720 3.55 0 2500 1000 3c 65 12 34 None 950 200 750 3.55 02500 1000 4a 65 12 11.25 None 962 200 761.5 4.4 0 2500 750 4b 65 1219.77 None 846 200 645.5 3.887 0 2500 750

TABLE 4b Process Conditions for Second Reactor Reactor Reactor CatalystCocatalyst C₂ C₂ C₂ H₂ C₄ C₆ Stirrer Ex- Temp. Pressure Flow Flow FlowVented Consumed Flow Flow Flow Speed ample ° C. bar umol/h g/h g/h g/hg/h g/h g/h g/h Rpm 1a 75 11 30 None 1350 600 750 0 15 2500 1000 1b 7511 30 None 1400 600 800 0 15 2500 1000 2  65 11 32.8 None 1075 380 695 040 2500 935 3a 75 11 32.8 None 1400 600 800 0 15 2500 1000 3b 75 11 24None 1380 600 780 0 15 2500 1000 3c 75 11 34 None 1350 600 750 0 15 25001000 4a 65 11 30 None 938 350 588 0 38 2500 750 4b 65 11 32.8 None 919380 539 0 37.7 2500 935

TABLE 4c Overall Process Conditions Flashtank R1/R2 Temp, Split, Example° C. %/% 1a 75 48.3/51.7 1b 75 42.9/57.1 2 75 46.3/53.7 3a 75 47.4/52.63b 75 48.0/52.0 3c 75 50.0/50.0 4a 75 50.5/49.5 4b 75 52.7/47.3

TABLE 5 Gas Analysis in First and Second Reactors First Reactor SecondReactor Ex- Butene Nitrogen Ethylene Hexane Hydrogen Ethane ButeneNitrogen Ethylene Hexane Hydrogen Ethane ample mol % mol % mol % mol %mol % mol % mol % mol % mol % mol % mol % mol % 2 0.00 1.17 94.58 1.461.34 0.00 0.47 0.56 95.07 1.81 0.02 0.00 3a 0.01 1.14 90.7 3.99 1.410.17 0.28 0.7 93.3 2.92 0.17 0.01 4a 0.00 0.83 92.35 3.02 1.27 0.22 0.420.82 91.33 4.49 0.03 0.15 4b 0.00 1.17 95.19 1.63 1.27 0.00 0.45 0.5495.05 2.43 0.02 0.00

TABLE 6 Production and Product Properties of Inventive Example RunProduct FTIR DSC Ex- Time Yield I₂₁ I₅ Density Butene Crystallinityample hours Kg g/10 min g/10 min I₂₁/I₅ g/cm³ mol % % RCD₁ 1a 12 6.5 10.32 31.4 0.9576 .475 77.76 Yes 1b 6 5.5 12.6 0.41 30.7 0.9591 0.5 77.53Yes 2  15 18 4.22 0.21 20.1 0.9501 ND 74 Yes 3a 10 5.8 8.50 0.4 21.30.9554 0.55 76.35 Yes 3b 12 5.5 7.75 0.3 25.2 0.9547 0.57 77.84 Yes 3c 73.8 8.37 0.4 20.9 0.954 0.69 74.34 Yes 4a 13 12 9.55 0.47 20.3 0.9518 ND68.8 Yes 4b 12 9 8.63 0.39 22.1 0.9504 ND ND Yes ND denotes “notdetermined”

TABLE 7 Product Properties of Inventive Examples and Comparative RunsInventive Inventive Inventive Inventive comparative comparative ExampleExample 1 Example 2 Example 3 Example 4 run 1 run 2 I₅ g/10 min. 0.270.20 0.42 0.41 0.21 0.40 I₁₀ g/10 min. ND 0.69 ND 1.37 0.85 ND I_(21.6)g/10 min. 5.28 4.36 8.75 8.14 6.21 9.39 I_(21.6)/I₅ 19.6 21.8 20.8 19.929.6 22.7 Density, g/cm³ 0.9668 0.9604 0.9640 0.9611 0.9640 0.9593 GPCM_(w) 216,500 229,900 209,000 200,800 239,200 ND GPC M_(w)/M_(n) 15.317.4 15.5 12.6 19.1 ND RCD Yes Yes Yes Yes No No Yield Stress, MPa 26.723.5 26.9 23.7 25.0 23.1 ND denotes not determined

As described in Tables 4-6, for Inventive Example 3, which consisted ofmelt-compounding three substantially equivalent polymerization runs toprovide sufficient quantities (i.e., Examples 3a, 3b and 3c), each runwas conducted in a manner similar to that described above for InventiveExample 1. Inventive Example 3 was stabilized and compounded with carbonblack in manner similar to Inventive Example 1 and, as described inTable 7, had an I₅ melt index of 0.42 g/10 minutes and a density of0.9640 g/cm³. As described in Tables 4-6, for Inventive Example 4, whichconsisted of dry blending two substantially equivalent polymerizationruns to provide sufficient quantities (i.e., Examples 4a and 4b), eachrun was conducted in a manner similar to that described above forInventive Example 1. Inventive Example 4 was stabilized and compoundedwith carbon black in manner similar to Inventive Example 1 and, asdescribed in Table 7, had an I₅ melt index of 0.41 g/10 minutes and adensity of 0.9611 g/cm³.

Comparative run 1 consisted of HOSTALEN CRP 100, supplied commerciallyby BASELL as a PE100 pressure pipe resin. Comparative run 1 had an I₅melt index of 0.21 g/10 minutes and a density of 0.9640 g/cm³ and isrecognized in the pressure pipe industry as the PE100 resin with thehighest hydrostatic strength. HOSTALEN CRP 100 is manufacturedexclusively with Ziegler-Natta catalyst in a dual reactor system.

Comparative run 2 consisted of a HDPE PE100 pressure pipe resin.Comparative run 2 had an I₅ melt index of 0.40 g/10 minutes and adensity of 0.9593 g/m³. Like CRP 100, this resin is manufactured using aconventional Ziegler-Natta catalyst system. Differential scanningcalorimetry analysis was performed using a Seiko DSC to determinecrystallinity and peak melting point.

Creep rupture tests were performed on a Frank type 68317 creep rigequipped with 15 sample stations. FIG. 2 shows the rig, except a frontand side view of only one sample station is illustrated and not all 15sample stations. The rig was equipped with an optical extensiometer forstrain measurements and with an oven to allow testing at elevatedtemperatures. Creep test samples (i.e., dogbones) were punched out ofcompression molded rectangular plagues having a nominal thickness ofabout 2 mm. The dimensions of the dogbone test bars were in accordancewith ASTM D412, specimen type C. The compression molding conditions forthe plaques were in accordance with ASTM D1928. The cross sectional areaof each individual test sample was measured separately to ensureaccuracy in calculation of the load to be applied to obtain the requiredstress level. In the testing, time to failure as well as creep behaviorwas monitored using the optical extensiometer mounted on the creep rig.To monitor creep behavior, two marker lines were drawn on the middlesection of the samples over their entire width at a distance of 35 mmapart. For testing at elevated temperatures, the oven was heated to thedesired temperature before test samples were placed therein. After theoven had equilibrated at a desired elevated temperature, it was switchedoff, the oven was opened and the samples were placed therein, then theoven door was closed and the oven was switched back on. This proceduretook 10-15 minutes wherein the oven reached thermal equilibrium quicklyafter placement of the samples. One hour after closing the creep ovendoor, zero strain was measured and the samples were loaded. Atappropriate times, the elongation of the sample was determined using theoptical extensiometer to obtain a creep curve. The time to failure wasmeasured with a timer that was operated by both a mechanical switch anda magnetic switch as shown in FIG. 2. The timer was only activated whenboth switches were in the “on” position. Each sample station in thecreep rig had its own timer.

Upon loading, the spring on top of the creep rig was squeezed causingthe mechanical switch to activate the timer. The metal strip on thebottom sample clamp kept the magnetic switch activated. As the metalstrip traveled downwards as the sample elongated during the testing, themagnetic switch stopped the timer at an elongation that depended on thepositioning of the strip on the clamp. An adjustable strip was mountedsuch that the timer switched off at an elongation of 200 percent. Thetimer allowed time to failure to be determined to an accuracy of 0.05hour.

TABLE 8 Actual and Calculated Creep Rupture Lifetimes at DifferentTemperatures and Stresses comp. Inventive comp. Inventive run 1 Example1 Inventive Ex. 1 Calculated Lifetimes run 2 Example 2 Inventive Example2 Calculated Lifetimes Temp. Stress Actual Actual Equation EquationEquation Actual Actual Equation Equation Equation ° Kelvin MPa LifetimeLifetime 1 2 3 Lifetime Lifetime 1 2 3 296 12.49 2483 3966 3494 34813472 ND 2590 ND ND ND 296 12.6 2406 3623 3379 3366 3358 1217 2620 16401634 1630 296 12.94 1670 ND 2294 2285 2280 568 1410 731 728 726 296 13.4450 1305 571 569 567 309 890 338 382 381 333 7.93 552 ND 1304 1635 18201320 10000 3288 4122 4589 333 8.17 700 2000 1678 2103 2342 300 ND 683856 953 333 8.34 350 1100 804 1008 1123 120 475 258 324 361 333 8.69 90320 190 239 266 ND 83 ND ND ND 353 6.3 225 4320 663 923 1080 552 ND 17192391 2798 353 6.37 215 6528 632 880 1029 313 2850 942 1310 1533 353 6.5422 969 56 78 92 140 200 401 558 653 353 6.68 30 135 32 109 127 10 119 2434 40 ND denotes not determined or calculated.

TABLE 9 Minimum Hoop Stress Requirements for PE100 Temperature HoopStress Min. Time to Failure ° C. MPa Hours 20 12.4 >100 80 5.5 >165 80 5>1000 

TABLE 10 Hoop Stress Performance Outside Minimum Hoop Failure InventiveTemp. Diameter Wall Thick- Pressure Stress Time Example ° C. mm ness mmbar MPa hours 2 20 32.00 2.85 24.22 12.39 >3397 2 60 31.90 2.81 15.508.02 >8088 2 60 31.90 2.66 14.51 7.98 >8088 2 60 32.00 2.78 14.517.63 >8088 2 60 31.95 2.86 14.91 7.58 >8088 2 80 31.80 2.79 10.595.51 >8088 2 80 31.85 2.86 10.79 5.47 >8088 2 80 32.00 2.80 9.615.01 >8088 2 80 31.82 2.79 9.61 5.00 >8088 2 80 31.97 2.82 9.514.89 >8088 3 20 31.90 2.78 23.73 12.43 >8040 3 60 31.90 2.88 15.89 8.005819 3 60 31.90 2.85 15.69 8.00 7412 3 60 31.90 2.81 14.71 7.61 >8040 360 31.90 2.82 14.71 7.61 >8040 3 80 31.90 2.89 10.98 5.51 2098 3 8031.90 2.90 10.98 5.49 1525 3 80 31.90 2.85 9.81 5.00 1936 3 80 31.902.86 9.81 4.98 4115 3 80 31.90 2.91 9.81 4.89 1967 4 20 32.00 2.80 23.7312.38 3372 4 60 32.00 2.82 15.50 8.02 4251 4 60 32.00 2.82 15.50 8.023271 4 60 32.00 2.80 14.51 7.57 >8064 4 60 32.00 2.78 14.51 7.63 >8064 480 32.00 2.81 10.79 5.60 >8064 4 80 32.00 2.81 10.59 5.50 >8064 4 8032.00 2.81 10.59 5.50 >8064 4 80 32.00 2.84 10.10 5.19 >8064 4 80 32.002.69 9.22 5.02 >8064 4 80 32.00 2.81 9.61 4.99 >8064 4 80 32.00 2.839.51 4.90 >8064

Table 8 compares the lifetimes of the different examples for stresses at23, 60 and 80° C. Comparing Inventive Example 1 to comparative run 1 andInventive Example 2 to comparative run 2, it is clear that for all ofthe tested stresses and temperatures, the lifetimes of the inventiveexamples were significantly longer than those of the comparative runs.

To describe the lifetime differences, the algebraic equations weredeveloped. For comparative run lifetime t₁, inventive example lifetimet₂ was longer at a given T (in Kelvin) as follows:

Preferably log t ₂≧1.0607×log t ₁+2.324−707/T  equation (1)

More preferably log t ₂≧1.0607×log t ₁+3.221−971/T  equation (2)

Most preferably log t ₂≧1.0607×log t ₁+3.649−1098/T  equation (3).

A comparison of the measured lifetimes of the inventive examples withcalculated lifetimes using equation 1-3 above is also given in Table 8.

For hoop stress comparisons, PE100 pressure requirements according toEuropean norm ISO/DIS 4437 are shown in Table 9. In addition to theabove creep rupture lifetime data, Table 10 shows that inventiveexamples also exhibit superior hoop stress when the hydrostatic strengthof pipe samples of 32 mm SDR 11 were measured according to ISO 1167.Accordingly, it is clear from Tables 8-10 that the inventive examplesfar exceed standard requirements for PE100 pressure pipe.

In another evaluation, two additional inventive examples were produced.These examples, Inventive Example 5 and 6, were manufactured in the samereactor system in a manner substantially equivalent to that describedabove for Inventive Example 1, including melt-compounding to increasesample quantities. But instead injection of fresh catalyst into eachreactor as was the case for Inventive Example 1, for these examples,fresh catalyst was injected into the first reactor only and no catalystwas injected into the second reactor. Also, process conditions wereadjusted such that the catalyst remained active in both reactors.Additionally, Inventive Examples 5 and 6 were identical except foradditive compounding. Table 11 provides the product and performance dataas well as the additive compounding data for these inventive examples.

The critical strain energy release rate GC was measured in the Charpymode in accordance with the procedure described by E. Plati and J. G.Williams in Polymer Engineering and Science, June 1975, Volume 15, No 6,pp. 470 to 477, the disclosure of which is incorporated herein byreference. For each temperature at least 6 samples are used. The sampledimensions are 125 mm×10 mm×10 mm. The bars are machined out of thickcompression molded sheets. The procedure used to mold these sheets was amodification of the procedure outlined in “A compression moldingtechnique for thick sheets of thermoplastics” by M. J. Cawood and G. A.H. Smith in Polymer Testing, 1 (1980), 3-7, the disclosure of which isincorporated herein by was used.

Thus samples were compression molded in a 10 mm thick mold, laterallyinsulated using Teflon™. The samples were heated up to 160° C. and keptat 6.7 MPa for three minutes followed by three one minute cycles ofexertion and release. Excessive flash was removed. The material was thenheated to 180° C. and kept for about 5 minutes at 6.7 MPa, which wasalso exerted and released for 3 cycles of one minute each. Finally, themelt was solidified under a pressure of 1.7 MPa and slowly cooledovernight by switching of the heating.

The Pennsylvania Notch Test (PENT), a slow crack growth test wasperformed following the procedure described by X. Lu and N. Brown,Polymer Testing, 11 (1992), pages 309-319, the disclosure of which isincorporated herein by reference. In the PENT method, a single edgenotched test specimen is exposed to a constant load at a well-controlledtemperature. The time to failure can be measured with a timer and therate of failure can be measured with a microscope or a dial gauge. Thenotch depth is generally about 35% of the sample thickness. The width ofthe notch may vary from about 15 to about 25 mm and the side grooves canvary from about 0.5 to about 1.0 mm depending on the width of thespecimen.

A notch is made in the sample by pressing a fresh razor blade into thespecimen at a speed of about 300 μ/min. At speeds of about 300 μ/minavoids notch tip damage and still provides a reasonably short notchingtime. At notching speeds of greater than about 525 μ/min, the failuretime is significantly increased. Notching speeds for the side grooves isnot particularly important. The apparatus should ensure that the notchand side grooves are coplanar.

During testing care should be taken to ensure that the specimen gripsappropriately arranged. To that end, the grips should be aligned andcentered with respect to the longitudinal axis of the specimen. Duringgripping the notch should not be activated by bending or twisting thespecimen. An alignment jig may be used to aid in properly gripping thespecimen to align the grips and avoid bending or twisting the specimen.In addition, the grips should have serrated faces to prevent slippageand the ends of the grips should be at least 10 mm from the notch.

The testing apparatus may be a direct loading device or a lever loadingdevice. A 5:1 a lever on ratio has been found to be very convenient. Thegrips may be attached to the loading machine by tabs which have auniversal action of that the applied to load is pure tension.

The applied stress is based on the unnotched cross-sectional area. Thevalue of the applied stress depends on the testing temperature. Therecommended value is that which produces brutal fracture as fast aspossible. Higher stresses produced ductile failure and lower stressesalong the testing time. For polyethylenes, the maximum stress forbrittle failure, the applied stress should have the values of 5.6, 4.6,4.2, and 2.4 MPa. at temperatures of 23, 42, 50, 80° C., respectively.In general, the stress for brittle failure by slow crack growth shouldbe less than one half the yield point in that particular testingtemperature.

The temperature should be controlled within ±0.5° C. It is notrecommended that polyethylene be tested above 80° C. because significantmorphological changes can occur during the test. Generally, depending onthe test temperature, a 1° C. change in the past temperature will changethe time to failure by about 10-15%.

A simple timer may be used to record the failure time. The timer shouldbe configured to switch off when the specimen fractures. The rate ofslow crack growth can be monitored with a microscope with a2-100×magnification by measuring the crack opening displacement versustime. A dial indicator which measures the overall extension of thespecimen can also detect the onset of crack initiation.

The PENT measurements reported herein were conducted at 2.4 MPa and 80°C. The sample dimensions were 50 mm×25 mm×10 mm and were machined fromthe same sheet as the G_(C) bars.

Viscosities were measured on a Rheometrics mechanical spectrometer (RMS)at 190° C. in the oscillatory mode.

Melt strength determinations are made at 190° C. using a GoettfertRheotens and an Instron capillary rheometer. The capillary rheometer isaligned and situated above the Rheotens unit and delivers, at a constantplunger speed of 25.4 mm/min., a filament of molten polymer to theRheotens unit. The Instron is equipped with a standard capillary die of2.1 mm diameter and 42 mm length (20:1 L/D) and delivers the filament tothe toothed take-up wheels of the Rheotens unit rotating at 10 mm/s. Thedistance between the exit of the Instron capillary die and the nip pointon the Rheotens take-up wheels was 100 mm. The experiment to determinemelt strength began by accelerating the take-up wheels on the Rheotensunit at 2.4 mm/s², the Rheotens unit is capable of acceleration ratesfrom 0.12 to 120 nm/s². As the velocity of the Rheotens take-up wheelsincrease with time, the draw down force was recorded in centiNewtons(cN) using the Linear Variable Displacement Transducer (LVDT) on theRheotens unit. The computerized data acquisition system of the Rheotensunit records the draw down force as a function of take-up wheel velocityin cN/sec. The actual melt strength value is taken from the plateau ofthe recorded draw down force in cN. The velocity at filament break wasalso recorded in cm/sec as the melt strength break speed.

TABLE 11 Product and Performance Properties of Inventive ExamplesInventive Example 2 5 6 Melt-Index I₅ g/10 min 0.21 0.25 0.25 I_(21.6)g/10 min 4.71 5.04 6.31 I_(21.6)/I₅ 22.43 20.16 25.24 Density g/cm³0.9511 0.9508 0.9508 Butene (FTIR) mole % 0.53 0.45 ND GPC M_(w) 229900223100 201400 M_(n) 13213 15200 15700 M_(w)/M_(n) 17.4 14.68 12,83 M_(z)832600 727200 RCD (Fractionation) Yes Yes Yes Calcium Stearate ppm 680Irganox ™ 1010 ppm 2080 845 329 Irgafos ™ 168 total ppm 2691 1900Irgafos ™ 168 remaining ppm 2784 2000 1723 DSC T_(o) ° C. 122.2 122.1121.2 T_(m) ° C. 133.2 134.4 133.1 Crystallinity % 72.77 68.11 69.0 OIT° C. min. 66 46 50 PENT min. >464484 >179796 >150000 G_(c) BrittleDuctile, ° C. 40 kJ/m² 23 kJ/m² 33 36.7^(d) 39.8^(d) 0 kJ/m² −5 −10kJ/m² 21.5^(d) 23.2^(d) −20 kJ/m² 18.4 17.7^(d) 21.0^(d) −30 kJ/m²17.1^(d) 17.4^(d) −40 kJ/m² 14.5^(d) 17.1^(d) −50 kJ/m² 13.6^(d)12.5^(b) −60 kJ/m² 12.8^(b) 12.0^(b) IZOD kJ/m² 545 44.6 44.7 Tensileproperties Yield stress MPa 23.1 23.7 24.8 Yield strain % 11.7 10.6 11.0Break stress MPa 36.6 42.4 42.2 Ultimate tensile stress MPa 36.6 42.442.2 Elongation % 673 683 697 Secant modulus MPa 556 622 614 Young'smodulus MPa 954 1044 957 3 point flex. modulus MPa 831 918 983 Rheologyviscosity @ .1/s 88371 86924 81283 viscosity @ 100/s 3100 2879 2680Power law k 37311 35654 34597 Power law N 0.50565 0.4972 0.4747Melt-Tension Screw rpm 27.9 27.0 Pressure Bar 107 115 V_(o) cm/sec 3.13.2 V_(z) cm/sec 46.0 53 M_(e) 13.84 15.56 Force cN 44.0 38.0 T_(z)cN/sec 8225 8675 Swell % 127 122 ^(b)indicates brittle failure modeobserved; ^(d)indicates ductile failure mode observed.

From data in Table 11, plots illustrating the low temperature ductilebreak point as well as the slow crack growth and rapid crack propagationperformances (based on G_(c) and PENT data) were prepared. FIG. 2 showsInventive Example 5 has an outstanding balance of slow crack growth andrapid crack propagation performance relative to PE80 and PE100standards. FIG. 3 shows Inventive Examples 2, 5 and 6 have excellent lowT_(db). Further, actual creep rupture testing was also performed onvarious inventive examples in direct comparisons with comparatives run 1and 2. FIG. 4 indicates that while at 80° C. and a stress of 5.8 MPa thelifetime for the comparative runs was approximately seven (7) days, thelifetime for Inventive Examples 2, 5 and 6 was extrapolated to 1400 days(i.e., 2,000,000 minutes or 33,000 hours).

In another evaluation, the differences between dual catalyst injectionand single catalyst injection were further investigated. In thisevaluation, Inventive Example 7 was manufactured via dual catalystinjection and Inventive Example 8 was manufactured via single catalyst.The same supported borate CGC catalyst system as used for InventiveExample 1 was used in each manufacture.

For Inventive Example 7, the polymerization was conducted continuouslyin a first continuously stirred autoclave tank reactor (CSTR), operatingat a liquid volume of 130 liter of hexane diluent. The catalyst wasinjected as a slurry using hexane as carrier into the liquid of thereactor. The reactor was controlled at a constant liquid temperature bycirculation of cold water in the cooling jacket of the reactor. Hexane,ethylene and hydrogen were fed to this first reactor. The melt index ofthe powder produced in the reactor was controlled by the hydrogen flowrate. The liquid volume of 130 liter was controlled by transferringslurry from the first reactor to a stripper.

The stripper had a liquid volume of 110 Liter and was operated at apressure of 0.4 barg and a temperature of 40° C. The temperature wascontrolled by circulation of cold water in the cooling jacket of thestripper, the pressure was controlled by venting of the stripper gasphase and a hexane feed rate of 60 L/Hr was used. In the stripper,substantially no polymerization takes place and undissolved hydrogen wasremoved from the liquid. The liquid volume of 110 liter of the stripperwas controlled by transferring the contents of the stripper to a secondCSTR configured sequentially with the first CSTR.

The second reactor was controlled at a temperature of 70° C. bycirculation of cold water in the cooling jacket of the reactor. Ethylenewas fed to the second reactor to control the split and butene ascomonomer was fed to the second reactor to control the density of theproduct. The same catalyst system as was fed to the first reactor wasalso separately fed to the second reactor. The melt index of the productproduced in the second reactor was controlled by controlling thehydrogen concentration in the reactor by continuous venting of the gasphase of the reactor. The liquid volume of 180 liter was controlled bydiscontinuously transferring slurry from the second reactor to afluidized bed drier, where powder product was separated from the liquidand unreacted monomers. The powder product was further dried using arotary drier to obtain a dry powder product. The run conditions arelisted in Table 12.

The dual reactor powder samples were dry blended with 2400 ppm IrganoxB215 and 750 ppm calcium stearate and then melt-compounded on aLeistritz compounding extruder operated at a temperature profile of 190to 220° C. at 30 kg/hr and 40 rpm (minimal specific energy). A nitrogenpurge was used to reduce the oxygen content as much as possible and theproduct was melt-compounded three times before the product evaluation.Inventive Example 8 was manufactured as described for Inventive Example7, except there was no catalyst feed to the second reactor.

In this evaluation, melt index and melt index ratios were determinedaccording to ASTM D-1238; the comonomer content was measured usingFourier Transform Infra Red (FTIR); the molecular weight distributionswere measured using high temperature GPC; slow crack growth performancewas assessed using PENT lifetime (Pennsylvania Notch Test); criticalstrain energy release rate, or G_(c), was determined as described above;and viscosity was measured using a Bohlin Constant Stress Rheometer inthe oscillatory mode at 190° C. wherein angular velocities were variedfrom 0.1 rad/s to 100 rad/s. The viscosity at 100 rad/s isrepresentative for the processability of the resin on fabricationequipment: the lower the viscosity, the easier the processability willbe. The viscosity at 0.1 rad/s is proportional to the melt strength ofthe material. The ratio of these two viscosities also gives anindication of the shear sensitivity of the material. The variousproperties of Inventive Examples 7 and 8, as compared to comparative run2, are presented in Table 13.

Table 13 indicates that the toughness, as measured by G_(c) at differenttemperatures, of Inventive Example 7 and Inventive Example 8 wasoutstanding as both were characterized by a very low ductile to brittletransition temperature close to −50° C. Also slow crack growthresistance, as determined by PENT, for both Inventive Example 7 andInventive Example 8 was excellent as both had PENT lifetimes of greaterthan 140,000 minutes. Thus, these resins have a unique balance of verylow ductile to brittle transition temperature and good resistance toslow crack growth.

To evaluate pipe performance, pipes of 32 mm SDR 11 were manufactured ofInventive Examples 7 and 8 and comparative run 2 on a Weber NE 45 pipeextruder. The extruder had a single 45 mm diameter screw and 30 D lengthfollowed by a standard PE layout comprising a Weber type PO 63 annularpipe die, two 6.6 m long cooling baths with vacuum calibration takingplace in the first bath, a caterpillar haul-off and a cutting unit.Fabricated pipes were then subjected to hydrostatic testing according toISO1167. The hoop stress results for the pipes are presented in Tables14-16.

From these data, regression analysis provided the following power lawequation for Inventive Example 7 which for a 50-year lifetime predicts afailure

TABLE 12 Run conditions Inventive Inventive Example 7 Example 8 R1Temperature ° C. 70 70 Pressure barg 5.9 1.9 Hexane flow rate L/Hr 70 70Ethylene flow rate kg/hr 8.9 8.1 Hydrogen flow rate NL/hr 34 26 Catalystflow rate g/hr 4.7 13.7 Production rate kg/hr 6.7 7.7 R2 Temperature °C. 70 70 Pressure barg 4.7 4.0 Hexane flow rate L/hr 40 — Ethylene flowrate kg/hr 10.6 9.3 Butene flow rate L/hr 0.64 0.73 Catalyst flow rateg/hr 4.7 — Vent flow rate kg/hr 2.0 0.5 Production rate kg/hr 7.4 8.0

TABLE 13 Product properties Inventive Inventive compara- Example 7Example 8 tive run 2 Melt index I₅ g/10 min 0.21 0.17 0.40 I₁₀ g/10 min0.79 0.66 I_(21.6) g/10 min 5.72 4.87 9.39 Ratio I_(21.6)/I₅ — 27.2428.65 22.70 Density g/cm³ 0.951 0.9493 0.9593 Comonomer mole % 0.45 0.55GPC Results M_(w) 226400 246800 M_(w)/M_(n) 15.61 15.14 RCD Yes Yes NoRheology Viscosity @ .1/s Pa.s 95622 109292 60703 Viscosity @ 100/s Pa.s2758 2860 2338 Tensile properties Yield stress MPa 24.25 24.09 23.08Tens Young's Modulus MPa 1013 1002 986 Flex Young's Modulus MPa 1014 921G_(c) Brittle Ductile 40° C. kJ/m² 45.5^(d) 48.5^(d) 23° C. kJ/m²36.6^(d) 43.6^(d) 11 0° C. kJ/m² 26.9^(d) 29.2^(d) −10° C. kJ/m²23.3^(d) 25.8^(d) −20° C. kJ/m² 22.1^(d) 22.7^(d) −30° C. kJ/m² 19^(d)20.5^(d) −50° C. kJ/m² 19.1^(d) 20.3^(d) −60° C. kJ/m² 14^(b) 14.8^(b)−70° C. kJ/m² 13.2^(b) 13.7^(b) Pent [SCG]minutes >142338 >200000 >10000 b: indicated brittle failure modeobserved

TABLE 14 Hoop stress results for Inventive Example 7 Temp., Stress,Failure time, Failure ° C. MPa hours Mode 20 12.9 845.56 Ductile 2012.95 762.27 Ductile 20 13 214.93 Ductile 20 13 86.6 Ductile 20 13.05672.33 Ductile 20 13.1 121.33 Ductile 20 13.2 81.71 Ductile 80 6 1484.85Ductile 80 6.3 1496.62 Ductile

TABLE 15 Hoop stress results of Inventive Example 8 Temp., Stress,Failure time, Failure ° C. MPa hours Mode 20 12.7 85.17 Ductile 20 12.7164.02 Ductile 20 12.75 235.78 Ductile 20 12.8 88.89 Ductile 20 12.8157.98 Ductile 20 12.85 67.41 Ductile 20 12.9 56.37 Ductile 20 12.9564.07 Ductile 20 13 33.21 Ductile 20 13 51 Ductile 80 5.5 1505.43Ductile 80 6.3 24.09 Ductile

TABLE 16 Hoop stress results for comparative run 2 Temp. Stress, Failuretime, Failure ° C. MPa hours Mode 20 13.06 65 Ductile 20 13.02 32Ductile 20 12.97 48 Ductile 20 12.97 72 Ductile 20 12.55 178 Ductile 2012.5 314 Ductile 20 12.45 208 Ductile 20 12.09 3120 Ductile 20 12.043120 Ductile 20 11.98 1285 Ductile 20 11.95 3762 Ductile 20 11.9 3120Ductile 20 11.74 9936 Ductile

stress above 12.5 MPa at 20° C. and thereby represents performance ofthe PE125 pressure class: Stress=13.4*time^(−0.005), with stress in MPaand time in hours.

For Inventive Example 7, no brittle failures were exhibited during hoopstress testing at 80° C., 5.8 MPa stress and >4000 hours. For InventiveExample 8, regression analysis predicts for a 50-year lifetime at 11.6MPa and 20° C. in accordance with the following power law equation,which represents performance of the PE112 pressure class:Stress=13.53*time^(−0.0118) with stress in MPa and time in hrs.

In another evaluation, the effect of providing a narrow MWD for thehigher molecular weight, lower density component was investigated.Comparative run 3 was prepared using the single reactor continuouslystirred-tank slurry polymerization with a Ziegler-Natta catalyst system.The catalyst was a non-decanted alkoxide (NDA) and the product wasproduced under process conditions presented in Table 15. The resultinghigh density product had an I₂ melt index of 94 g/10 minutes and adensity of 0.9719 g/cm³ and was produced at a total pressure of 12 bars,a hexane feed rate of 1500 g/hr of hexane, an ethylene supply rate of816 g/hr ethylene and a hydrogen fed rate of 140 Nliters/hr and thereactor was operated at an average residence time of 82 minutes.

Comparative run 4 was prepared with the same catalyst system ascomparative run 3 using different process conditions as presented inTable 17. Comparative run 4 was an ethylene/1-butene copolymer and hadan I_(21.6) melt index (Condition 190° C., 21.6 kg) of 0.38 g/10 minutesand a density of 0.9306 g/cm³. Comparative run 4 was produced at a totalpressure of 12 bars, a hexane feed rate of 2800 g/hr, an ethylene supplyrate of 856 g/h, a hydrogen supply rate of 7.2 Nl/h and a butene supplyrate of 200 g/hr and the reactor was operated at an average residencetime of 48 minutes.

Comparative run 5 was a product sample taken immediately after the firstreactor of a two-reactor slurry polymerization system. Comparative run 5was a high density product, low molecular weight product and had an I₂melt index of 118 g/10 minutes and a density of 0.9720 g/cm³.

Comparative run 6 was produced using a supported constrained geometrycatalyst system, designated herein as “CGC”, as described above forInventive Example 1. Comparative run 6 was manufactured insingle-reactor slurry polymerization system using a 26 L CSTR(continuous stirred tank reactor) with adequate stirring to keep theparticles in suspension. The reactor was jacketed to remove the heat ofreaction and a constant flow of 5900 g/h of propane was fed to thereactor and a constant flow of nitrogen was fed into the vapor space ofthe reactor. The reactor over pressure was controlled by venting the gasand 2500 g/h of ethylene and 4.96 NL/h of hydrogen were injected belowthe liquid level using a common pipe. The CGC catalyst was injected,along with liquid propane diluent, below the liquid level. The CGCcatalyst concentration in the catalyst vessel was 0.8 wt. % in hexaneand solids were withdrawn intermittently. For the manufacture, thereactor temperature was held at 70° C. and pressure was held at 55 barg.The reactor was operated at an average residence time of 60 minutes andthe resulting polymer production rate was 714 g/h while the catalystefficiency was calculated to be 170,813 g PE/g Ti. Details of theprocess conditions used to manufacture comparative run 6 can be found inTable 14. Comparative run 6 was a high density product and had an I₂melt index of 119 g/10 minutes and a density of 0.9731 g/cm³.

Comparative run 7 was produced using the same catalyst system andpolymerization system as comparative run 6, except 163.4 g/h of hexenewas fed to the reactor and hydrogen flow was very low and was dilutedwith nitrogen. The average residence time for the manufacture ofcomparative run 7 was 60 minutes and the polymer production rate was 441g/h while catalyst efficiency was calculated to be 150,000 g PE/g Ti.Comparative run 7 was an ethylene/1-hexene copolymer and had an I_(21.6)melt index of 0.25 g/10 minutes and a density of 0.9235 g/cm³.

Product properties for comparative runs 3-7 can be found in Table 18.For abbreviation purposes of this investigation, the broad MWD componentwas designated as NDA, as it is made using the non-decanted alkoxyide,conventional Ziegler-Natta catalyst system. The narrow MWD component wasdesignated as CGC, as it was made using a constrained geometry catalystsystem. The expression “NDA/CGC” then means that the low MW fraction hada broad MWD and the high MW fraction had a narrow MWD. NDA/NDA, CGC/NDAand CGC/CGC are the other designations used in this investigation.

Comparative run 8 was made by dry blending comparative run 3 andcomparative run 4 at a ratio of 48:52 (NDA/NDA). This material had abroad MWD LMW and broad MWD HMW. To this mixture, 500 ppm Calciumstearate and 2250 ppm IRGANOX B215 were added. The mixture was thenextruded on a small APV twin screw extruder using a melt temperature of220° C. and a melt pressure of 35 to 50 bar at 200 rpm. The resultingoutput was approximately 2.6 kg/hr and the specific energy of theextrusion was 0.24 kWh/kg. Also, a nitrogen purge was placed on theextruder feed hopper to avoid or minimized the possibility of oxidativecrosslinking.

Inventive example 9 was made by dry blending comparative run 6 andcomparative run 4 at a ratio of 48:52. The resulting mixture, CGC/NDA,had a narrow MWD LMW component and a broad MWD HMW component. As a firstpass, the mixture was melt-extruded at a low temperature (140° C.) andlow throughput (0.4 kg/hr) on a small 60 mm Goettfert single screwextruder. In a second pass, the mixture was melt-compounded on an APVtwin screw extruder using the same conditions.

Inventive example 10 was made by dry blending comparative run 5 andcomparative run 7 at a ratio of 48:52. This resulting mixture, NDA/CGC,had a broad MWD LMW component and a narrow MWD HMW component. As a firstpass, this mixture was melt-extruded at a low temperature (140° C.) andlow throughput (0.4 kg/hr) on a small 60 mm Goettfert single screwextruder. In a second pass, the mixture was melt-compounded on an APVtwin screw extruder using the same conditions.

Inventive example 11 was made by dry blending powder of comparative run6 and comparative run 7 a ratio of 48:52. This mixture, CGC/CGC, had anarrow MWD LMW component and narrow MWD HMW component. As a first pass,this mixture was melt-extruded at a low temperature (140° C.) and lowthroughput (0.4 kg/hr) on a small 60 mm Goettfert single screw extruder.In a second pass, the mixture was melt-compounded on an APV twin screwextruder using the same conditions.

TABLE 17 Process conditions and gas analysis for Single Reactor ProductsExample comp. run 3 comp. run 4 comp. run 6 comp. run 7 Catalyst NDA NDACGC CGC Process Conditions P [barg] 12 12 55 55 T deg C. 88 70 70 70 C₆flow [g/h] 1501 2800 Propane flow [g/h] 5902 5902 Tau [min] 82 48 60 60Gas Analysis N₂ [V %] 0.87 0.8533 77.11 78.14 H₂ [V %] 69.47 4.746 0.040.002 C₂ [V %] 19.89 82.206 10.70 11.56 C₂H₆ [V %] 1.07 0.04052 C₄ [V %]0.01 5.152 Isopentane [V %] 0.01 0.7445 C₆ [V %] 1.44 9.452 0.07 0.03C₃H₆ [V %] 0.22 0.2034 C₃H₈ [V %] 0.01 0.009156 12.50 10.80 H₂/C₂ gasphase ratio [mol %/mol %] 3.511 0.057733012 0.003383 0.000173 C₄/C₂ gasphase [mol %/mol %] 0.000 0.062671824 Process Flows C₂ flow start [g/h]68.66 230 2497.00 2497.00 H₂ flow [Nl/h] 140.42 7.213 4.96 0.00 C₂ flow[g/h] 816.23 856.475 2497.00 2497.00 C₄ flow (AK 3) [g/h] 0.00 199.941hexene flow [g/h] 0.00 163.44 Catalyst flow [micromolTi/h] 62.06 21.287.36 61.30 Hexane flow [g/h] 207.90 71.02 5902 (C3), 896 (C6) 5902(C3), 628.3 (C6) Product Properties Powder (before Melt Index, I₂ g/1094 100 compounding) min Melt Index, I_(21.6), 0.38 0.33 g/10 minDensity, g/cm³ 0.9306 0.9285

TABLE 18 Product Properties comp. run comp. run comp. run comp. runcomp. run Example 3 4 5 6 7 Catalyst NDA NDA NDA CGC CGC I₂ g/10 min. 950.36 118 119 0.25 DSC T_(o) ° C. not avail not avail 125.0 127.4 108.8T_(m) ° C. not avail not avail 132.1 135.3 124.2 Crystallinity % notavail not avail 85.1 86.81 51.49 GPC M_(n) 7370 82500 3970 133700 137200M_(w) 26500 389200 44400 355900 345300 M_(n)/M_(w) 3.6 4.72 11.18 2.662.52 RCD No No No No Yes Density g/cm³ 0.9719 0.9298 0.9720 0.97310.9235

TABLE 19 Product Performance Properties Comp. run Inventive Ex InventiveEx Inventive Ex Example 8 9 10 11 Mixture 48%/52% NDA/NDA CGC/NDANDA/CGC CGC/CGC Melt Index I₅ g/10 min. 0.32 0.43 0.27-0.27 0.31I_(21.6) g/10 min. 8.64 9.97 4.11-4.09 5.24 I_(21.6)/I₅ Ratio 27.0023.19 15.22-15.15 16.90 Density g/cm³ 0.9519 0.9528 0.9506 0.9505 RCD NoNo Yes Yes Bohlin Rheology viscosity @ .1/s Pa.s 74251 60151 66489 61290viscosity @ 100/s Pa.s 2298 2110 3006 3085 Power law K 28047 23925 3206730370 Power law n 0.4817 0.5077 0.5304 0.5439 Tensile properties Yieldstress MPa 25.4 25.1 24.7 24.6 Young's modulus MPa 1072 1011 946 960 3Point Flex. Young's MPa 986 910 837 848 modulus Izod Impact kJ/m² 22.117.1 34.7 42.7 Rapid Crack propagation Gc ductile - brittle  20 kJ/m²14.8 21.4 24.0 38.9  0 kJ/m² 10.9  −5 kJ/m² 9.6 −10 kJ/m² 8.8 10.5 20.9−15 kJ/m² 7.5 8.5 −20 kJ/m² 6.6 11.8 7.6 19.3 −30 kJ/m² 6.4 10.0 17.3−40 kJ/m² 7.7 12.9 −50 kJ/m² 7.3 10.4 −60 kJ/m² 6.3 10.3 T_(db) ° C. −12−35 −17 −45 Slow Crack Growth Minutes 59700 16362 >110000 >110000 PENTGPC M_(n) 11700 14100 7660 19700 M_(w) 198800 271600 233100 218900M_(w)/M_(n) 16.99 19.26 30.43 11.11 M_(z) 797100 2183000 757000 732600

Product properties (reported in Table 19) were determined in thisinvestigation as disclosed in EP 089 586 and WO 01/005852 and thecritical strain energy release rate was determined as described above isused.

Table 19 clearly indicates that in a comparison of comparative run 8 toInventive Example 9 that changing the LMW component from a broad to anarrow MWD (when the HMW component has a broad MWD) surprisinglyincreases the G_(c) from 14.8 to 24.1 kJ/m², and that T_(db) decreasesfrom −12° C. to −35° C. Further, a comparison of Inventive Example 10 toInventive example 11 shows that changing the LMW component from a broadto a narrow MWD (when the HMW component has a narrow MWD), increasesG_(c) from 24 to 38.9 kJ/m², and that T_(db) decreases from −17° C. to−45° C.

As demonstrated above, embodiments of the invention provide a newpolyethylene composition which is useful for making water and gas pipesand various other articles of manufacture. The new composition has oneor more of the following advantages. First, the new composition hasbetter durability. In some instances, exceptional durability is achievedby certain compositions. However, the improved durability is notachieved at the expense of toughness. Certain compositions exhibit goodtoughness and durability. As such, articles made from the newcompositions should have longer service lives. Because the newcomposition comprises at least two components, desired properties of theoverall composition may be obtained by adjusting the characteristics ofeach component, such as MWD, average molecular weight, density,comonomer distribution, etc. Therefore, it is possible to design adesired composition by molecular engineering. Other characteristics andadditional advantages are apparent to those skilled in the art.

While the invention has been described with respect to a limited numberof embodiments, the specific features of one embodiment should not beattributed to other embodiments of the invention. No single embodimentis representative of all aspects of the inventions. Moreover, variationsand modifications therefrom exist. For example, the polyethylenecomposition may comprise a third component, either ethylene homopolymeror copolymer, which makes the composition tri-modal in the overallmolecular weight distribution. Similarly, a fourth, fifth, or sixthcomponent may also be added to adjust the physical properties of thecomposition. Various additives may also be used to further enhance oneor more properties. In other embodiments, the composition consistsessentially of the LMW component and the HMW component described herein.In some embodiments, the composition is substantially free of anyadditive not specifically enumerated herein. In certain embodiments, thecomposition is substantially free of a nucleating agent. Cross-linkingby physical or chemical methods may be another way to modify thecomposition. The appended claims intend to cover all such variations andmodifications as falling within the scope of the invention.

We claim:
 1. A polyethylene composition comprising alow-molecular-weight (LMW) ethylene homopolymer component and ahomogeneous, high-molecular-weight (HMW) ethylene interpolymercomponent, wherein the LMW component is characterized as having amolecular weight distribution, MWD^(L), of less than about 8 and aweight average molecular weight, M_(w) ^(L), and wherein thepolyethylene composition is characterized as having a bimodal molecularweight distribution, and a ductile-brittle transition temperature,T_(db), of less than −20° C.
 2. The polyethylene composition of claim 1,wherein the LMW component has a density of greater than about 0.965g/cm³.
 3. The polyethylene composition of claim 1, wherein the LMWcomponent has an I₂ value ranging from about 30 to about 1000 g/10minutes as determined in accordance with ASTM D-1238 (Condition 2.16kg/190° C.).
 4. The polyethylene composition of claim 1, wherein the HMWcomponent has a density ranging from about 0.905 to about 0.955 g/cm³.5. The polyethylene composition of claim 1, wherein the HMW componenthas an I_(21.6) value ranging from about 0.1 to about 1.0 as determinedin accordance with ASTM D-1238 (Condition 21.6 kg/190° C.).
 6. Thepolyethylene composition of claim 1, wherein the HMW component has anI_(21.6) value ranging from about 0.1 to about 0.6 as determined inaccordance with ASTM D-1238 (Condition 21.6 kg/190° C.).
 7. Thepolyethylene composition of claim 1, wherein the HMW component has anI_(21.6) value ranging from greater than 0.6 to about 1.0 as determinedin accordance with ASTM D-1238 (Condition 21.6 kg/190° C.).
 8. Thecomposition of claim 1, wherein the HMW is characterized by a unimodalmolecular weight distribution, MWD^(H) of about 8 or less and a weightaverage molecular weight M_(w) ^(H).
 9. The composition of claim 8,wherein M_(w) ^(H)/M_(w) ^(L) is about 1.3 or higher.
 10. Thecomposition of claim 1, wherein MWD^(L) is about 5 or less.
 11. Thecomposition of claim 1, wherein MWD^(L) is about 3 or less.
 12. Thecomposition of claim 1, wherein MWD^(L) is about
 2. 13. The compositionof claim 8, wherein MWD^(H) is about 5 or less.
 14. The composition ofclaim 8, wherein MWD^(H) is about 3 or less.
 15. The composition ofclaim 8, wherein MWD^(H) is about
 2. 16. The polyethylene composition ofclaim 1, wherein the polyethylene composition is characterized as amolecular weight distribution (MWD) as defined by the ratio ofM_(w)/M_(n) of about 30 or less, and the HMW component is characterizedas having a substantially uniform comonomer distribution or a reversecomonomer distribution.
 17. The composition of claim 16, wherein the HMWcomponent has a substantially uniform comonomer distributioncharacterized by a SCBDI of greater than 70 percent.
 18. The compositionof claim 16, wherein the HMW component has a reverse comonomerdistribution characterized as the molar comonomer content ofinterpolymer fractions having a M_(w) greater than or equal to 300,000g/mole being at least 25 percent higher than the molar comonomer contentof interpolymer fractions having a Mw of less than or equal to 100,000g/mole.
 19. The composition of claim 1, wherein the T_(db) is less thanabout −25° C.
 20. The composition of claim 1, wherein the T_(db) is lessthan about −30° C.
 21. The composition of claim 1, wherein the T_(db) isless than about −40° C.
 22. The composition of claim 1, wherein theT_(db) is less than about −50° C.
 23. The composition of claim 1,wherein the molecular weight distribution, M_(w)/M_(n), of thecomposition is less than or equal to 20, as determined using gelpermeation chromatography.
 24. The composition of claim 1, wherein thecomposition is characterized as having an I_(21.6)/I₅ ratio of less thanor equal to 22.5, as determined in accordance with ASTM D-1238(Condition 21.6 kg/190° C. and Condition 5 kg/190° C).
 25. Thecomposition of claim 1, wherein the composition is characterized ashaving an I_(21.6) ranging from about 3 to less than about 50 g/10 min.,as determined in accordance with ASTM D-1238 (Condition 21.6 kg/190°C.).
 26. The composition of claim 1, wherein the composition ischaracterized as having an I_(21.6) ranging from about 3 to about 12g/10 min., as determined in accordance with ASTM D-1238 (Condition 21.6kg/190° C.).
 27. The composition of claim 1, wherein the composition ischaracterized as having an I_(21.6) ranging from about 12 to less thanabout 50 g/10 min., as determined in accordance with ASTM D-1238(Condition 21.6 kg/190° C.).
 28. The composition of claim 1, wherein thecomposition is characterized as having an I₅ ranging from about 0.1 toabout 2 g/10 min., as determined in accordance with ASTM D-1238(Condition 5 kg/190° C.).
 29. The composition of claim 1, wherein thecomposition is characterized as having a density greater than about0.938 g/cm³.
 30. The composition of claim 1, wherein the composition ischaracterized as having a M_(v1)/M_(v2) ratio of less than or equal to0.6, where M_(v1) is the viscosity average molecular weight of the LMWhigh density component and M_(v2) is the viscosity average molecularweight of the HMW interpolymer component, as determined using ATREF-DVanalysis.
 31. The composition of claim 1, wherein the composition ismanufactured using a multiple reactor slurry polymerization system. 32.The composition of claim 31, wherein the polymerization system comprisestwo autoclave reactors.
 33. The composition of claim 32, wherein the tworeactors are configured in series.
 34. The composition of claim 33,wherein a supported metallocene catalyst system is used.
 35. Thecomposition of claim 34, wherein catalyst is separately injected intoeach reactor.
 36. The composition of claim 34, wherein the catalystsystem is injected into the first reactor and no catalyst is injectedinto the second reactor such that polymerization in the second reactoris accomplished from carry-over catalyst or live polymer or both fromthe first reactor.
 37. The composition of claim 34, wherein themetallocene catalyst is a constrained geometry catalyst.
 38. Thecomposition of claim 35, wherein the catalyst is a constrained geometrycatalyst system.
 39. The composition of claim 34, wherein the samecatalyst is separately injected into each reactor.
 40. The compositionof claim 39, wherein the catalyst is a constrained geometry catalystsystem.
 41. The composition of claim 34, wherein the catalyst systemcomprises an activator which has been bonded or fixed to the supportprior to the addition of the metallocene catalyst.
 42. The compositionof claim 41, wherein the activator is a boron-containing compound. 43.The composition of claim 41, wherein the activator is an alumoxane. 44.The composition of claim 1, wherein the HMW component is characterizedas having a reverse comonomer distribution.
 45. The composition of claim44, wherein the reverse comonomer distribution is characterized by acomonomer distribution gradient in the range from about 0.0001 to about0.1.
 46. The composition of claim 44, wherein the reverse comonomerdistribution is characterized by a comonomer distribution gradient inthe range from about 0.0005 to about 0.05.
 47. The composition of claim44, wherein the reverse comonomer distribution is characterized by acomonomer distribution gradient in the range from about 0.001 to about0.02.
 48. The composition of claim 1, wherein the M_(w)/M_(n) of thecomposition is about 25 or less.
 49. The composition of claim 1, whereinthe M_(w)/M_(n) of the composition is between about 5 and about
 20. 50.An article of manufacture made from the composition claim
 1. 51. Thearticle of claim 50, wherein the article is a water pipe.
 52. Thearticle of claim 50, wherein the article is a gas pipe.